Advertisement
Glossary of Drug Discovery and Development Terms

Numbers | A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z |

 
3'
The end of a nucleic acid chain that terminates in a free hydroxyl group.

5'
The end of a nucleic acid chain that terminates in a free phosphate group.

ATop
A-DNA
The dehydrated form of right-handed helical DNA obtained under non-physiological conditions.

ab initio gene prediction
The prediction of exon structure within a gene using computational algorithms. Exons are ligated to form the structural protein that is encoded by the gene.

Abiotic
The absence of living systems.

Abzyme
An antibody engineered to carry out an enzymatic reaction;a catalytic antibody. Typically the antibody is raised against a transition state analog for the reaction to be catalyzed.

Accession number
The unique identifier assigned to new sequence information submitted to a major database.

Acclimatization
The adaptation of an organism to new environmental conditions.

Achiral
A compound that may be superimposed on its mirror image. Achiral molecules do not display topological handedness.

Acquired mutation
A non-heritable genetic change occurring within a somatic cell; a somatic mutation.

Acrocentric
Describes a chromosome with a centromere near the end.

Activated complex
The molecular assembly that corresponds to the transition state of a chemical reaction.

Activator
A protein that up-regulates gene expression by binding to transcription control sites.

Active immunity
The natural immunological response to an antigen.

Active site
The catalytic site of an enzyme.

Active transport
Vectorial transport of a molecule or ion against a concentration gradient by a membrane-bound protein complex.

Adaptation
The change in the response of a system over time; functional or structural changes that allow an organism to respond to changes in the environment.

Adduct
The covalent complex formed when a chemical binds a biomolecule, such as DNA or a protein.

Adenine
A purine that is one of the five bases found in nucleic acids.Adenine base pairs with thymine in DNA and with uracil in RNA.

Adeno-associated virus
A virus used to construct vectors that introduce genes into cultured cells.

Adenocarcinoma
A cancer of the epthelial cells that form the ducts of glandular organs.

Adenoma
A benign tumor formed by an increase in the number of epithelial cells that form the ducts of glandular organs.

Adenosine
A nucleoside form of adenine.

Adenosine triphosphate (ATP)
A nucleotide that releases energy upon hydrolysis of the phosphate bonds. The energy stored in ATP may drive synthetic processes; be converted to mechanical, light, or electrical energy; or be released as heat.

Adenovirus
A group of non-enveloped icosahedral viruses. Recombinant forms of adenovirus are used as gene delivery vectors.

Adjuvant
A substance that enhances or diversifies the immune response; a drug that modulates the actions of other drugs.

ADME
Procedures for evaluating the absorption, distribution, metabolism, and elimination of pharmaceuticals.

Adult stem cell
A stem cell derived from adult bone marrow. Like embryonic stem cells, adult-derived cells may differentiate into multiple cell types.

Affinity
A measure of the binding strength between two molecules.

Affinity chromatography
A chromatographic method used to isolate biomolecules that reversibly bind a molecule attached to a solid-phase support.

Affinity tag
An amino acid sequence added to a recombinant protein to facilitate purification of the expressed protein.

Agarose
A carbohydrate polymer used as a matrix for electrophoresis.

Aglycon
The non-carbohydrate component of a glycoside.

Agonist
A ligand that binds a receptor at a site adjacent to the active site.

Agrobacterium tumefaciens
A bacterium that is used for plant genetic engineering.

Algorithm
An explicit computational procedure that uses a precise sequence of simple operations to perform a complex operation. Bioinformatics algorithms enable processing, analysis, and visualization of sequence-related data.

All-or-none
A reaction or response that occurs fully or not at all.

Allele
A variant form of a given gene that occupies a specific chromosomal locus.

Allelic exclusion
The expression of genes from the maternal or paternal chromosome but not both, due to chromosomal inactivation. In B-lymphocytes, allelic exclusion assures that all antibodies expressed are derived from the same allele.

Allergen
A chemical or protein antigen that induces an allergic reaction. Allergens typically increase the plasma concentration of IgE which induces mast cells to release histamine.

Allergy
An inflammatory immune response to a nonpathogenic antigen.

Allogenic, allogeneic
Genetic differences between individuals of the same species.

Allograft
A graft of tissue between two genetically different members of the same species.

Allosteric transition
Reversible modification of protein structure and activity by an effector molecule that binds at a site other than the active site.

Allosterism
The ability of an effector molecule (ligand) to change the conformation and activity of a protein.

Allotype
A protein variant arising from genetic differences between individuals of the same species.

Allozyme, alloenzyme
One of the different forms of an enzyme found in individuals of the same species, due to the presence of multiple alleles in the population.

Alpha helix
A helical configuration formed by a protein chain in which successive turns are held together by hydrogen bonds between the peptide links.

Alternative splice form
One of the set of proteins with related sequences (isoforms) that may be generated by alternate splicing of exons within a single mRNA.

Alternative splicing
The process by which alternative exons within a single RNA are combined during the splicing process, resulting in the generation of mRNAs encoding different protein sequences. Alternative splicing may be tissue- or disease-specific.

ALU sequence
A 3-5% component of the human genome, consisting of 300-bp repetitive DNA sequences containing an Alu 1 restriction site.

Amber codon
The UAG codon, one of three codons that code for termination of transcription of an mRNA and release of the newly synthesized polypeptide chain from the ribosome.

Amino group
The -NH2 group, a weakly basic group found in organic molecules.

Amino terminus
The end of a polypeptide that contains a free amino group; the N-terminus.

Aminoacyl site (A site)
One of two sites in the large ribosomal subunit involved in protein translation. The aminoacyl site binds the incoming aminoacyl-tRNA during protein synthesis.

Aminoacyl-tRNA
A tRNA charged with the appropriate amino acid. The amino acid is esterified to the 3' end of the tRNA. Aminoacyl-tRNAs function as ribosomal adaptors during translation of mRNA into protein.

Aminoacyl-tRNA synthetase
An enzyme that catalyzes the attachment of the appropriate amino acid to the 3' end of a tRNA.

AMP
The abbreviation for adenosine monophosphate; also written as 5' AMP, since the phosphate is attached to ribose moiety at position 5.

Amphipathic helix
An alpha helix that is hydrophobic on one side and hydrophilic on the other.

Amphipathic, amphiphilic
Describes a molecule containing both hydrophobic and hydrophilic regions.

Amphitrophic
Capable of photosynthetic or chemotrophic growth.

Ampholyte, carrier ampholyte
One of a set of small electrolytes with differing isoelectric points used to establish a pH gradient in gels.

Amphoteric
Describes a molecule that reacts as an acid with bases, and as a base with acids.

Amphotropic Virus
A virus that infects a wide range of mammalian host cell types.

Amyloid
Proteins with beta sheet structure that form extracellular aggregates.

Anabolic
An energy-requiring biochemical process that synthesizes complex molecules from simpler reactants.

Anaerobe
Any microorganism that grows in the absence of molecular oxygen.

Analog
A molecule that is structurally and functionally related to another molecule.

Analogy
The deduction of the function of a new gene or protein by comparison with genes or proteins of known function using similarity searching and alignment.

Anamnestic reaction
An increase in immune response following repeated exposure to an antigen.

Anaphase
The stage of nuclear division when chromatids (homologous chromosomes) move to the poles of the mitotic spindle.

Anaphylaxis
Extreme immune sensitivity produced upon the reintroduction of an antigen.

Anaplasia
The reversion of a cell to a simpler, undifferentiated form.

Anaplerotic metabolic pathway
A biochemical pathway that replenishes intermediates needed by a central metabolic pathway.

Anergy
A deficient immune response due to inactivated B- and T-lymphocytes.

Angiogenesis
The formation of new blood vessels during embryogenesis, tissue repair, or tumorigenesis. Development of anti-angiogenic agents is a focus of anti-cancer strategies.

Angiostatin
A plasminogen fragment with anti-angiogenic properties.

Angstrom
A unit of measure used to measure inter-atomic distances within molecules equal to 10-10 meter.

Anion
An ion with a negative charge. Anions migrate to the anode of an electrophoretic gel.

Annotation
Analysis and commentary added to sequence data in databases. Annotation provides in-context information about coding and non-coding sequence within genes, patterning and motifs, similarities, known or predicted protein structure and function, as well as links to external data, such as clinical observations.

Anode
The positive electrode of an electrophoretic system toward which anions migrate.

Antagonist
Ligands that bind to the active site on a protein.

Anti-idiotype antibody
An antibody that recognizes and is complementary to the binding site of another antibody.

Anti-oncogene
A tumor suppressor gene.

Antibody (Ab)
A glycoprotein produced by B-lymphocytes of vertebrates capable of recognizing and reversibly binding an antigen. Antibodies consist of four protein chains (two heavy chains and two light chains) and a polysaccharide moiety.

Antibody combining site
The antigen (epitope) recognition and binding site of an antibody. The variable regions of both heavy and light chains contribute to the antibody combining site.

Antibody directed enzyme prodrug therapy (ADEPT)
A two-step treatment protocol that involves the administration of an inactive prodrug that is subsequently activated in a target-specific manner by an antibody linked to an enzyme that activates the prodrug.

Antibody mimetic protein
Proteins selected by directed molecular evolution that have high affinity for a molecular target.

Anticodon
Three-nucleotide sequence of a transfer RNA (tRNA) that is complementary to the three-nucleotide codon of an mRNA.

Antifreeze protein
A glycoprotein found in serum of artic fish that prevents ice crystals from forming.

Antigen (Ag)
A molecule, molecular assembly, or organism that is specifically recognized by an antibody.

Antigen mimic
An unrelated protein that resembles an antibody target protein and cross-reacts with the antibody.

Antigen presenting cell (APC)
A cell that recognizes an antigen to be neutralized, processes it, and incorporates the resulting peptides into the major histocompatibility complex (MHC) molecules on the cell surface. The resulting MHC-peptide complexes are then presented to T-lymphocyte for destruction.

Antigenic determinant
A specific region of an antigenic molecule that binds an antibody (epitope). The antigenic determinants of proteins are typically peptides.

Antihormone
A substance that attenuates the response to hormones.

Antimetabolite
A substance that prevents utilization of a metabolite.

Antimitotic
An agent that decreases the rate of mitosis.

Antimorph
A mutant gene that produces the opposite effect of the wild-type gene at the same locus.

Antimutagen
An agent that decreases the rate of mutation.

Antimutator gene
A mutant gene that reduces the rate of mutation.

Antineoplastic
A drug that reduces or prevents the growth of a neoplasm.

Antioxidant
A compound that inhibits oxidation, often because it is preferentially oxidized. Antioxidants trap free radicals, breaking the chain of reactions and preventing damage to cell components.

Antiparallel
Parallel linear structures with directional polarity. DNA strands in double-stranded DNA are antiparallel.

Antiporter
A transmembrane exchange protein that transports two different molecules in opposite directions across a membrane.

Antisense
Complementary in sequence to an RNA molecule.

Antiserum
Serum that contains a high level of antibodies against a specific antigen.

Antisuppressor
A mutation that reduces the effects of a gene expression suppressor.

Antiterminator
A protein that prevents RNA synthesis termination and allows RNA polymerase to continue transcribing genes.

Anucleate
Lacking a nucleus.

Apical surface
A plasma membrane region of epithelial cells that faces the lumen and is involved in transport.

Aplastic
Incomplete growth or development of a structure.

Aplysia
A small marine organism widely used for neurobiological studies.

Apoenzyme
The protein part of an enzyme, without prosthetic groups or cofactors.

Apolipoprotein
The protein component of a lipoprotein.

Apoprotein
The protein component of a conjugated protein.

Apoptosis
A programmed or controlled form of cell death characterized by the loss of cell junctions and microvilli, condensation of the cytoplasm, margination of the nuclear chromatin, and fragmentation of the nucleus.

Aptamers
Short strands of DNA that bind protein targets. Decoy aptamers inactivate DNA-binding proteins, such as transcription factors, resulting in the activation or inactivation of genes.

Apurinic site
A DNA site from which the purine base has been lost by cleavage of the glycosidic linkage.

Apyrase
An enzyme with ATPase and ADPase activity used to deplete ATP in reactions.

Arabidopsis thaliana (A. thaliana)
A small plant used as a model organism for the study of plant genetics.

Arachidonic acid
Eicosatetraenoic acid, a precursor for the synthesis of signaling molecules, such as prostaglandins and thromboxanes. Arachidonic acid is released from cell membrane phospholipids, including phosphatidyl inositol, by phospholipases.

Array synthesis
A form of parallel synthesis used in combinatorial chemistry in which the reactions take place in a spatially organized array.

Arrayed library
Two-dimensional arrays of recombinant clones. Each primary clone is identified by row and column.

Arthus reaction
A complement-dependent hypersensitivity reaction that occurs when an antigen reacts with a precipitating antibody, forming microprecipitates that damage cells.

Artificial chromosome
A minimal chromosome assembled from cloned DNA sequences and coding for an origin of replication, a centromere, and telomeres.

Ascites
An accumulation of fluid in the peritoneal cavity. When due to the growth of a hybridoma, the ascites fluid contains a high concentration of monoclonal antibodies.

Aseptic
Procedures that prevent the contamination of cultures, media, animals, and persons by extraneous microorganisms.

Assay
A procedure for detecting the presence, estimating the concentration, and determining the biological activity of a macromolecule, molecule, ion, or cell. Assays are based on measurable parameters that enable the evaluation of differences between samples and controls. Sensitivity, the ability to detect small amounts of a substance, and specificity, the ability to detect only the analyte, are essential features of an assay.

Assembly
The compiling of overlapping gene sequence fragments into a single, continuous sequence.

Association constant (Ka)
The measure of the degree of association of a complex. The larger the Ka, the more tightly the components are bound.

Astrocyte
A glial cell found in the brain with a star-like shape. Astrocytes provide physical and metabolic support for neurons.

Astrocytoma
A tumor arising from astrocytes, glial cells found in the brain.

Atomic force microscopy (AFM)
A form of scanning probe microscopy that provides atom-level information about molecules. The surface of a molecule is scanned with a microprobe in an x-y grid, and the force encountered is measured with piezoelectric sensors.

Attenuated vaccine
A vaccine based on an attenuated virus that has low virulence due to genetic inactivation or chemical treatment.

Attomole
One quintillionth mole; 10-18 mole.

Auto-
A prefix that indicates self-origin.

Autoimmune response
The response of the immune system to normal tissues, cells, or molecules within the body.

Autologous
Derived from the same organism.

Autonomously replicating sequence (ARS)
A plasmid sequence that confers the ability to replicate in a yeast cell.

Autoradiography
A technique that uses x-ray film to detect radiolabeled molecules following separation by gel electophoresis. Recently autoradiographs have been supplanted by nonradioactive methods based on the detection of chemiluminescence.

Autosome
A chromosome not involved in sex determination. The human genome consists of 22 pairs of autosomes, and one pair of sex chromosomes.

Autotroph
A microorganism that synthesizes all organic molecules from inorganic sources.

Auxotroph
A microorganism strain that requires nutrients not required by the wild-type strain.

Avidin
A glycoprotein that binds with high affinity to biotin.

Avidity
A measure of the affinity of the binding of an antibody to an antigen.

Axon
A long part of a cell that transmits nerve impulses from the neuron cell body to the axon terminus, resulting in neurotransmitter release.

BTop
B cell
A B-lymphocyte.

B-DNA
The fully hydrated right-handed helical form of DNA seen in vivo.

Bacille Calmette-Guerin (BCG)
An attenuated form of a mycobacterium that activates the immune system. BCG extracts are used in adjuvants to stimulate the immune response.

Bacillus thuringiensis (B. thuringiensis, B.t.)
A microorganism that produces a protein that acts as a biopesticide.

Bacteria
Unicellular prokaryotic organisms that lack a membrane-bounded nucleus.

Bacterial artificial chromosome (BAC)
A vector capable of replication in bacteria that is used to clone 100 to 300 kb DNA fragments into E. coli cells.

Bacteriophage (phage)
A virus that infects bacterial hosts, and may be utilized to introduce genes. Phage are widely used as cloning and expression vectors.

Baculovirus
A viral pathogen, such as Autographa californica, that replicates in lepidopteran larvae. Baculovirus expression vectors are widely used for the synthesis of proteins that require post-translational modifications.

Baculovirus expression system
A cellular protein synthesis system based on recombinant baculovirus vectors that is capable of post-translational processing of proteins. Translated proteins are glycosylated, acylated, and proteolytically cleaved in the cytoplasm of the lepidopteran cell.

Bait protein
One of two hybrid proteins used in two-hybrid protein-protein interaction assays.

Barr body
A single condensed X chromosome. The Barr body is found in the nuclei of female somatic cells.

Basal cell
A relatively undifferentiated cell in an epithelial sheet that forms more specialized cells.

Basal cell carcinoma
A non-metastatic cancer derived from the basal cells of the epithelium.

Basal lamina
A proteoglycan and glycoprotein sheet secreted by cells to form the extracellular matrix. The basal lamina, also called the basement membrane, is a three-layer structure that influences cell polarity, differentiation, and migration.

Base pair (bp)
A unit of nucleic acid length, based on the number of paired bases (adenine and thymine, guanine and cytosine) in a DNA double helix.

Base sequence
The order of nucleotide bases in a DNA molecule.

Base stacking
The stacking of base pairs in parallel planes within the interior of a helical double-stranded nucleic acid.

Basic local alignment search tool (BLAST)
A nucleic acid and protein sequence comparison program based on the creation of a matrix of similarity scores for all possible pairs of residues, defining the high-scoring segments, and statistically evaluating the significance of the results.

Basolateral surface
The region of the cell plasma membrane adjacent to the basal lamina.

Basophil
A multinucleated leucocyte characterized by cytoplasmic granules that release histamine and other hypersensitivity response effectors.

Bead-based array
A microarray technology based on the attachment of individual probes to microbeads. The beads may be embedded in the microwells formed at the tip of a bundle of optical fibers.

Bence-Jones protein
Free immunoglobulin light chains synthesized by myeloma cells.

Benign tumor
A tumor that is not cancerous and does not metastasize.

Beta barrel
A protein structural element consisting of antiparallel beta strands that forms a hydrophobic protein core.

Beta bend
A protein structural element consisting of a hairpin turn between two beta strands.

Beta configuration
A protein configuration in which two beta strands are hydrogen bonded to each another.

Beta sheet
The protein configuration resulting from the alignment of multiple adjacent beta strands and the formation of hydrogen bonds between them.

Beta strand
A protein region, from 5 to 10 residues in length, in an almost fully extended conformation.

Bidirectional replication
Replication of DNA in two directions from the origin of replication.

Bilamellar
Consisting of two layers, often used in reference to lipid bilayer structures.

Bioassay
An assay that uses a living system, such as an intact cell, as a component.

Biocatalysis
The use of biological systems or their components for chemical synthesis or transformation.

Biochips
Micro-scale systems for bioanalysis based on integrated circuit technology. Biochips include molecular microarrays (gene chips, protein chips, small molecule chips), microfluidics systems (lab-on-a-chip), and fiber-optic-based arrays.

Biocide
A compound that is toxic to living systems.

Biocombinatorial chemistry
An iterative process consisting of synthesis of combinatorial chemical libraries followed by screening in biological systems to evaluate function.

Biocontrol, biological control
The control of one species by another, as in biological pesticides.

Bioconversion
The conversion of one chemical to another by a living system, such as a bacterial cell.

Biodegradable
A material that can be broken down to simpler components by a biological process.

Biodiversity
The genetic diversity of natural organisms. Collections of millions of microbial genomes harvested from global ecosystems are the starting point for developing new processes and molecules.

Bioelectronics
The study of intermolecular electron transfer in biological processes. A recent application of bioelectronics is the design of systems that use organic molecules to form electronic circuit elements that detect and quantify target molecules.

Bioequivalent
A pharmaceutical compound that equals another in bioavailability and potency.

Biogenesis
The theory that living systems arise only from pre-existent living systems.

Bioinformatic sequence markup language (BSML)
A data markup language that is a container for bioinformatics data. The goal is to integrate data from multiple platforms and make it possible to interact with and visualize the data. BSML is a form of XML, extensible markup language.

Bioinformatics
Computational or algorithmic approaches to the analysis and integration of genomic, proteomic, or chemical data residing in databases. Bioinformatics includes applications for the analysis of DNA and protein sequence patterns.

Bioleaching
The recovery of precious metals from ore by biological processes.

Biolistics
The high-velocity injection of DNA-coated particles directly into tissues, cells, or organelles using a gene gun.

Biological response modifier (BRM)
A protein or other compound that stimulates immune defense against disease.

Biological therapy
Therapies that stimulate the immune system to fight disease.

Bioluminescence
Production of light by a chemical reaction within an organism. Bioluminescence generated by firefly luciferase is a sensitive assay for ATP, which is utilized during the reaction. Chemiluminescence differs in that it involves a synthetic substrate.

Biomacromolecule
A large biological molecule, such as DNA or protein.

Biomarker
A molecular marker associated with a biological function.

Biomass
The mass of material produced by living micoorganisms, plants, or animals.

Biomaterial
Biologically derived material that is utilized as a structural component.

Biome
An ecological community of organisms and environments.

BioMEMS
The application of microelectromechanical systems (MEMS) to micro- and nanosystems for genomics, proteomics, and drug delivery analysis; molecular assembly; tissue engineering; biosensor development; and nanoscale imaging.

Biometrics
The statistical study of biological events.

Biomimetics
The development of synthetic systems based on information from biological systems.

Biomineralization
The deposition of minerals by microorganisms and plant and animal cells.

Bionics
The use of information derived from living systems to build electromechanical systems.

Biont
A single organism.

Bionucleonics
The study of the application of isotopes to living systems.

Biophotonics
Biological applications of photonics, a technology that utilizes light and other forms of radiant energy in which a quantum unit is the photon.

Biophysics
The application of the techniques of physics to biological processes.

Biopolymer
A protein, nucleic acid, or polysaccharide molecule.

Bioprocess
A method for preparing biological products, for commercial use.

Bioprospecting
Searching for new plant and microbial strains that may serve as sources for natural products, such as phytopharmaceuticals.

Bioreactor
A container used for fermentation or enzymatic reactions. Bioreactors vary in size from benchtop fermentors to standalone units.

Biosemiotics
The study of the exchange of information between organisms.

Biosensor
A device that uses a biological element, such as an immobilized enzyme or cell, as a sensor.

Biosorption
The sequestering of chemicals by a biological system.

Biostatistics
A specialized branch of applied statistics that deals with the statistical evaluation of experimental research or clinical trial results.

Biosurface
The surface structure of individual molecules, cells, and more complex biological systems.

Biosynthesis
Synthesis by a living system.

Biotechnology
Biological techniques applied to research and product development.

Biotherapy
Treatment with genetically engineered biological materials.

Biotin
A small molecule that binds with high affinity to avidin and streptavidin. Biotin is used to label nucleic acids and proteins that may be subsequently detected by avidin or streptavidin linked to a fluorescent or enzymatic reporter molecule.

Biotinylation
The covalent linkage of biotin to DNA and proteins. Biotin may be detected with avidin or streptavidin linked to an enzymatic moiety or fluorescent molecule.

Bispecific antibody
An engineered antibody with two different binding sites that recognize two different antigens.

Bivalent
Having two sites available for binding.

Blast cell
An undifferentiated embryonic cell.

Blood-brain barrier
A semipermeable membrane that controls diffusion of molecules into the cerebrospinal fluid.

Blue gene
A massively parallel supercomputer with 1 million processors that is under construction and will be capable of 1 petaflop floating point operations/sec. Blue gene is specifically engineered for use in biomolecular simulations.

Blunt ends
Flush DNA ends generated by restriction enzymes that cut both DNA strands at the same point.

Blunt-end ligation
The joining of DNA ends that have no overhang by a DNA ligase.

Boc
A symbol for a protecting group used in polypeptide chemistry.

Bone marrow
The tissue in the middle of a bone that is involved in the proliferation and differentiation of stem cells to produce blood cells (hematopoiesis).

Booster
A secondary immunization used to increase a weak immune response to a primary immunization.

Buffer
A solution containing agents that maintain a constant pH during a biochemical reaction.

Building block
A reagent used in combinatorial library synthesis.

Bystander effect
Secondary effects on adjacent cells and tissues triggered by treatment of a primary target with a therapeutic agent.

CTop Caenorhabditis elegans (C. elegans)
A nematode widely used in cell lineage studies.

Cage carrier
An ionophore that surrounds an ion during transport.

Cancer
A disease characterized by uncontrolled proliferation of cells.

Cap structure
A specialized nucleotide structure present at the 5' end of mRNA consisting of a methlyguanosine residue linked by a triphosphate bridge to the 5' end of the RNA. The cap protects the structure and facilitates transcription initiation.

Capillary electrophoresis (CE), capillary zone electrophoresis
A rapid, high-resolution electrophoresis method based on free zone electrophoresis in tubes of less than 1 mm dia.

Capsid
The protein coating of a free virus particle.

Capsule
The polysaccharide outer layer of some bacteria. Also, a connective tissue sheath that encloses a tissue or organ.

Carboxyl group
The acidic -COOH functional group found in organic molecules.

Carboxyl terminal, C-terminus
The end of a polypeptide that contains a free carboxyl group.

Carcinogen
A molecule that can transform normal cells into cancer cells.

Carcinogenesis
The transformation of normal cells into cancer cells.

Carcinoma
A cancer that arises in epithelial tissue.

Carrier protein
A protein that confers immunogenicity to small molecules (haptens) that are not themselves immunogenic.

Cascade
A sequence of successive activation reactions.

Cassette
Genetic material that is spliced into a genome.

Catabolism
An energy-releasing biochemical process that degrades complex molecules into simpler products.

Catabolite activator protein (CAP)
A bacterial transcription factor that is activated by cAMP.

Catabolite repression
The repression of transcription of the components of a biosynthetic pathway due to the accumulation of the degradation products of the metabolite produced by the pathway.

Catalytic antibody
An antibody engineered to catalyze an enzymatic reaction. Typically the antibody is raised against a transition state analog for thereaction to be catalyzed.

Cathode
The negative electrode of an electrophoretic system toward which cations migrate.

Cation
An ion with a positive charge.

Caviola (plural, caviolae)
Plasma membrane-attached vesicles involved in endocytosis.

CCD camera
A camera that uses CCD (charge coupled device) chips to convert photons to electrical or digital information.

CD array
A microfluidics-based array in compact disc format that utilizes centrifugal force to transport molecules through microchannels.

cDNA (complementary DNA)
A single-stranded DNA molecule that is complementary in base sequence to an RNA strand.

cDNA library
A collection of cloned DNA molecules complementary to the complete set of mRNAs obtained from a cell, tissue, or organism.

Cecropin
A basic polypeptide with antibacterial activity.

Cell array
A microarray consisting of living cells.

Cell culture
The process of growing and maintaining cells and cell lines; a form of tissue culture.

Cell division cycle
The DNA synthesis pattern in dividing cells. The cell division cycle consists of four phases: G1 (Gap), S (Synthesis), G2 (Gap), and M (Mitosis). DNA replication occurs during the S phase and chromosomal separation occurs during the M phase.

Cell fusion
The formation of a single hybrid cell from two cells in response to treatment with a fusogen.

Cell mapping
The localization of proteins within organelles or protein complexes by purification of the organelle or complex followed by mass spectrometric identification of the components.

Cell membrane
The lipid bilayer plasma membrane that forms the cell boundary.

Cell motility
The movement of eukaryotic cells generated by contractile elements of the cytoskeleton. Cells move by protrusion of cell processes, formation of focal contacts, and retraction of the trailing edge. Motility of bacterial cells is due to cilia and flagella.

Cell proliferation
The increase in cell number due to growth and division.

Cell-free expression system
A mRNA-programmable protein synthesis system.

Cell-mediated immunity
The immune response mediated by T lymphocytes. Cell-mediated immunity is responsible for allograft rejection, delayed hypersensitivity, and defense against viruses.

Centimorgan (cM)
A measure of the frequency of genetic recombination. A centimorgan is a unit of genetic mapping equal to 1% crossover of genes between homologous chromosomes as established by genetic studies.

Centromere
The chromosomal region to which spindle fibers attach when cells divide.

Chaotropic agent
An ion that dissolves membranes, solubilizes proteins, and denatures nucleic acids. Chaotropes, such as guanidium isothiocyanate,are widely used to denature ribonucleases during RNA isolation.

Chaperone
A protein that binds newly synthesized polypeptide chains to prevent incorrect folding during transport to protein assembly sites.

Chelator
A molecule that binds metal ions.

Chemical fingerprinting
The analysis of low molecular weight components of a cell by techniques, such as mass spectrometry, gas chromatography, and HPLC.

Chemical genetics
The use of small molecules to interact with proteins in order to identify the genes involved in a biochemical pathway.

Chemical genomics
The large-scale study of biological processes based on small-molecule intervention.

Chemical markup language (CML)
A computional language for the management of chemical data.

Chemical proteomics
A method for defining the function of proteins by screening proteins against libraries of small molecules.

Chemiluminescence
The production of light by a chemical reaction.

Chemiluminescent immunoassay (CLIA)
An immunoassay that utilizes a signal generated by light-releasing reactions.

Cheminformatics
Informatics technologies that integrate chemical data with analytic and molecular design tools. Cheminformatics applications provide access to compound-related information, including chemical structure, properties, structure-activity relationships.

Chemo-autotroph
A microorganism that obtains energy from light-independent inorganic reactions.

Chemogenomics
The integration of genomic, biological activity, and drug molecule data with pharmacology and toxicology information.

Chemokine
A small, soluble protein with a wide range of immunoregulatory functions.

Chemostat
Device for maintaining a bacterial population in the exponential growth phase by controlling nutrient input and cell removal.

Chemotaxis
The movement of a cell or organism in response to a chemical gradient.

Chimera
An organism combining tissues derived from two or more genotypes.

Chimeric antibody
A recombinant antibody that combines characteristics of antibodies from two different sources (see Humanized antibody).

Chimeric DNA
A hybrid DNA molecule generated by the ligation of DNA restriction fragments from different sources. Transcription and translation of the chimeric DNA plasmid results in a chimeric protein.

Chimeric protein
A hybrid protein produced by recombinant DNA technology from a chimeric DNA molecule.

Chiral
A compound that cannot be superimosed on its mirror image.

Chiral resolution
The resolution of a mixture of D- and L-enantiomers of a chiral compound.

Chiral synthesis
The production of one enantiomer of a chiral compound, often by stereospecific synthesis by an enzyme.

CHO
A cell line derived from the ovary of the Chinese hamster that is used for cytogenetic studies because of the small number of chromosomes.

Chomosome painting
The identification of chromosomes using combinatorially labeled fluorescent chromosomal probes in a wide array of colors. The chromosomal painting probes specifically hybridize with chromosome sequences and identify known bands.

Chromat
A DNA sequencer output data file consisting of fluorescent traces for each base and the DNA sequence.

Chromatid
One of the two daughter strands of a duplicated chromosome.

Chromatin
The network of chromosomes, histones, and other proteins found in the eukaryotic nucleus during interphase. The euchromatin corresponds to regions in which the chromosomes are dispersed, and the heterochromatin to the regions in which chromosomes are condensed.

Chromatography
The separation of a mixture of substances by charge, size, or other property by allowing the mixture to partition between a moving phase and a stationary phase.

Chromatophore
Pigment-containing cells within the dermis of fish and amphibians.

Chromogen
A molecule with a chromophore that is colorless until the chromophore is modified chemically.

Chromophore
A functional group that absorbs light, giving rise to color.

Chromoprotein
A protein that contains a chromophore, a molecule that absorbs light.

Chromosomal marker
A physical location on a chromosome in which the inheritance may be monitored. A marker may be a restriction site or a gene.

Chromosomal translocation
The translocation of a chromosome fragment to another chromosome.

Chromosome
A structure that carries the heriditary information for an organism and consists of a long DNA molecule with associated proteins.

Chromosome banding
A chromosome identification method based on the production of a band pattern by staining.

Chromosome jumping
A technique for isolating non-contiguous clones from a genomic library by jumping regions between known points on the chromosome.

Chromosome walking
A strategy for locating a gene based on sequencing a panel of overlapping clones that span the estimated location of a gene.

Cilia
Hair-like structures composed of bundled microtubules that drive fluid across the surface of a cell, or drive cell movement.

Circadian
A biological activity with a periodicity of 24 hrs that is independent of environmental variation.

Cis-acting
Describes transcription-factor binding sequences that regulate the transcription of a structural gene located on the same strand of DNA.

Cisterna
Flattened membrane-bound compartment found in the endoplasmic reticulum and Golgi.

Cistron
A segment of DNA that codes for a single protein chain.

Clade
A taxonomic subgroup with similar traits identified by cladistics.

Cladistics
A classification method that constructs phylogenies using characteristics unique to each taxonomic group.

Cladogenesis
An adaptive evolutionary process that leads to the development of a greater variety of organisms.

Class I proteins
Major histocompatibility antigens that enable the immune system to distinguish self. Also known as transplantation antigens.

Class II proteins
Major histocompatibility antigens that are found only on the surface of specific lymphocyte cell types and some macrophages.

Class switch
A change in the class of antibody expressed by B lymphocytes (i.e., from IgG to IgM).

Clinical informatics
The use of informatics to evaluate clinical trial design and to design electronic systems for protocol and data storage.

Clinical trial
The evaluation in humans of the effectiveness of a new drug therapy. The phases of a clinical trial are: Phase I, the evaluation of the safety of the drug; Phase II, the determination of optimal dosage and effectiveness; and Phase III, the large-scale evaluation.

Cloned animals
Multiple genetically identical animals generated by reproductive cloning techniques.

Cloned cells
Multiple identical cells produced by natural cell division processes.

Cloned DNA
Exact copies of a DNA segments prepared using recombinant DNA technology.

Cloning vector
Plasmid or bacteriophage element used to transfect a recipient cell with a DNA fragment that is replicated (cloned).

Clonotypic
Characteristic of a clone.

Clustering
A bioinformatics technique for visualizing patterns in experimental data.

Clusters of differentiation (CD) antigens
A nomenclature used to standardize the naming of human leukocyte differentiation antigens located on the cell surface and recognized by monoclonal antibodies.

Coding region (CDS)
The genomic sequence between start and stop codons.

Codon
Three-nucleotide sequence in mRNA that directs the incorporation of a specific amino acid into the protein chain.

Coenzyme
A small molecule associated with an enzyme that participates in enzymatic catalysis.

Cofactor
Inorganic ion or coenzyme necessary for the activity of an enzyme.

Cohesive ends
The single-stranded extensions generated in double-stranded DNA by staggered cuts by restriction endonucleases. Cohesive ends are also known as sticky ends.

Coiled coil
The form of the DNA helix in vivo, in which DNA structures are twisted around each other.

Cold-shock protein
A protein expressed at low temperatures that protects cell components. For example, CspA, a cold-shock protein of E. coli, binds RNA and prevents secondary structure formation.

Colicin
Bacterial proteins that are toxic to closely related strains of bacteria.

Colony stimulating factor (CSF)
A cytokine that controls the differentiation of hematopoietic stem cells in the bone marrow and elsewhere.

CombiChem
Informal term for combinatorial chemistry.

Combinatorial biology
The use of libraries of recombinant microbes to produce complex natural products.

Combinatorial chemistry
A technique for systematically assembling molecular building blocks in many combinations to create thousands of diverse compounds.

Common object request broker architecture (CORBA)
Specifications for an object computing infrastructure that automates network tasks and enables the interoperability of diverse database systems, such as those used to warehouse bioinformatics data.

Comparative genomics
The comparison of genomes and of distinct sequences within a genome. Comparative genomics makes possible the application of information gained from a simple genome to a more complex genome, and is the basis for the understanding of genetic variation within a species.

Competent cells
Pretreated bacterial cells that facilitate DNA transfection.

Competitive immunoassay
An assay based on the competition of labeled antigen and unlabeled antigen (from the sample) for antibody binding sites.

Complement
A plasma protein system involved in immune defense. Following activation by antigen-antibody complexes, complement proteins lyse antigenic cells, attract phagocytic cells, and assist in the destruction of antigenic cells by phagocytosis.

Complementarity
The reverse structural correspondence of one molecule to another, such as an antibody to an antigen, an enzyme to a substrate, or the bases in a base pair.

Complementarity determining region (CDR)
The variable regions of an antibody molecule that form the antigen binding site. The CDR is formed by the combined variable regions of both light and heavy chains.

Complementary DNA (cDNA)
DNA synthesized from an mRNA template.

Complementary sequence
DNA or RNA sequence that can base pair with another sequence to form a double-stranded structure.

Complex molecular assembly
Multimolecular structure held together by noncovalent bonds.

Complexity
The study of complex phenomena in natural systems. Basic themes include the dynamics, interactions, emergence, adaptation, learning, and evolution of a system.

Computational biology (bioinformatics)
Computational technologies for the collection, structuring, and mining of biological data that make possible prediction and knowledge discovery.

Computational chemistry
Computer-based modeling and prediction of the structure of chemical compounds most likely to bind a protein drug target. Known properties are used to calculate properties of new molecules and energy minimization is used to adjust the structure.

Computer-assisted drug design (CADD)
Computational techniques to design and optimize biologically active compounds with desired structure and properties.

Computer-assisted molecular modeling (CAMM)
Computational techniques for the exploration and visualization of molecular structures and properties.

Confocal microscopy
A light microscope technique that constructs an image from information derived from point-by-point scanning of a field.

Conformation
The spatial determinants of the atoms within a molecule, for example, the 3-D shape of a protein.

Congenic
Organisms that differ in genotype at a single locus.

Conjugated proteins
Proteins conjugated to other molecules, such as lipids, carbohydrates, heme, or synthetic labels.

Connexin
A subunit of connexon, a multi-subunit transmembrane channel protein that forms bridges between adjacent cells at gap junctions.

Connexon
A multi-subunit transmembrane channel protein that forms bridges between adjacent cells at gap junctions.

Consensus sequence
A sequence pattern derived from the alignment of multiple sequences that represents the nucleotide or amino acid most likely to occur at each position in a sequence.

Conservation
The retention of sequence and 3-D structure by biomolecules under varying environmental and genetic conditions.

Conservative change
An alteration of the amino acid sequence of a protein with no effect on the function of the protein.

Constitutive
Produced in a constant amount, not subject to regulation. Housekeeping genes are constitutively transcribed.

Contig
A group of cloned pieces of DNA representing overlapping regions of a chromosome.

Contig map
A map depicting the relative order of a series of small overlapping clones representing a chromosomal segment.

Contiguous genes
A set of genes that are located together on a chromosome and are capable of functioning as a unit to express a trait.

Contrast agent
A compound used for in vivo 3-D mapping of tissues by magnetic resonance imaging (MRI).

Control
A standard of comparison by which experimental results are evaluated. A control differs from the experiment in a single variable, and enables the assessment of significance of experimental results.

Control element
A gene region that binds transcription regulatory factors.

Convergence
The endpoint of an iterative or recursive algorithm. Convergence is reached when the difference between predicted and observed data is less than a preset threshold.

Cooperativity
A phenomenon by which the binding of a ligand to one site of a receptor or enzyme alters the affinities of the other sites.

Corepressor
A metabolite that combines with and activates a repressor, resulting in the repression of transcription of a gene.

Cosmid
A phage lambda-based vector used for cloning large DNA fragments (45 kb) into E. coli cells.

Covalent bond
A stable bond between atoms based on the sharing of electrons.

CpG island
A DNA region characterized by methlyated cytosine residues in the sequence CpG. Methlated cytosines are correlated with reduced expression of genes.

Cre-Lox system
A phage-based system for the site-specific insertion and deletion of DNA. Tissue-specific knockouts may be generated in transgenics using the Cre-Lox system.

CREB-binding protein (CBP)
A transcriptional co-activator of phosphorylated CREB (Cyclic AMP Response Element Binding Factor).

Critical micelle concentration (CMC)
The lowest concentration of a detergent at which molecules aggregate to form micellar structures.

Cross reactivity
The binding by an antibody of an antigen that is structurally similar to the antigen that the antibody was raised against.

Cross-flow filtration
A technique for filtering thick fluids by flowing the fluid across the filter. The fluid phase becomes more concentrated without blocking the filter.

Cross-sectional study
The study of a population at a point in time. Cross-sectional studies are also known as horizontal studies.

Crossing over
Reciprocal exchange of corresponding segments between homologous chromosomes, resulting in recombination of genetic elements.

Cryopreservation
A process for storing biological material at very low temperatures for lengthy periods of time. Mixed solvents containing glycerol and dimethyl sulfoxide are used to protect cells from ice crystal formation.

Cryoprotectant
A molecule that prevents the formation of ice crystals in frozen cells. Glycerol, dimethyl sulfoxide (DMSO), and sucrose are widely used as cryoprotectants. Antifreeze proteins also have cryoprotectant effects.

Cryptotope
An immunological determinant that is hidden.

Crystal structure
A structure obtained by x-ray diffraction analysis of a crystal consisting of an ordered array of biomacromolecules.

Culture collections
Large repositories of microorganisms and cell lines, maintained by institutions and countries. Culture collections serve as sources of organisms for scientists, and as a record of ownership for the depositor.

Curated database
A database developed by a curator with domain expertise. Curators remove redundancy from submitted data, incorporate annotations, and add reference information and links to external databases.

Curation
The process of verifying and enhancing data submitted to bioinformatics databases. Curators verify automated annotation of data, and add in-context descriptions of molecular, biochemical, and cellular function.

Curing agent
An agent that eliminates plasmids from a cell.

Cyclic adenosine monophosphate (cAMP)
A 'second messenger' molecule generated from AMP by adenyl cyclase following activation by a G-protein.

Cyclic AMP response element binding factor (CREB)
A leucine zipper transcription factor that is activated by cAMP.

Cyclooxygenase (COX)
An enzyme involved in thromboxane and prostaglandin synthesis. Inhibition of COX is responsible for the anti-inflammatory action of non-steroidal anti-inflammatory drugs (NSAID), such as ibuprofen and aspirin.

Cyclosporin
An immunosupressant used in transplant surgery to prevent rejection of transplants.

Cytidine
A nucleoside form of cytosine.

Cytochrome
A heme-containing protein involved in electron-transfer reactions.

Cytogenetics
The study of the appearance, structure, and behavior of chromosomes.

Cytokine
A member of a family of proteins released by cells that act on other cells through specific receptors. Cytokines control cell growth and differentiation, and regulate immune and inflammatory responses. Examples of cytokines include growth factors and colony-stimulating factors.

Cytoplasm
All the protoplasm of a living cell outside the nucleus and inside the plasma membrane.

Cytosine
A pyrimidine derivative that is one of the five bases found in nucleic acids. Cytosine base pairs with guanine.

Cytoskeleton
An integrated protein framework within eukaryotic cells that provides shape, internal spatial organization, and motility.

Cytosol
The part of the cytoplasm external to the subcellular organelles.

Cytotoxic T cell
A T-lymphocyte subset that recognizes a specific antigen presented by an MHC Class I molecule, and lyses the cell.

DTop D-
A configurational prefix that designates one of two chiral configurations (see L-).

Dalton
A unit of molecular mass approximately equal to the mass of a hydrogen atom.

Data cleaning
Computational processing to remove noise and artifacts from digital data prior to storage.

Data mining
The automated or semi-automated search for relationships and global patterning within data. Data mining techniques include data visualization, neural network analysis, and genetic algorithms.

Data warehouse
A collection of databases combined with a flexible data extraction system.

De novo sequencing
DNA or protein sequencing techniques that do not depend on any prior knowledge of the sequence.

De-orphaning receptors
Determining the ligands that bind orphan receptors.

Deconvolute
To simplify or render less complex.

Deconvolution
An algorithm-based method for eliminating noise and improving the resolution of digital data. For example, deconvolution algorithms are used to remove out-of-focus haze from confocal microscope images.

Degranulation
The release of cellular granule contents.

Delayed fluorescence immunoassay
(DELFIA) A fluorescence technique based on the use of a molecule with a long fluorescence half-life.

Deletion
The loss of genetic material from a gene or a chromosome.

Deletion mapping
The use of overlapping deletions to determine the location of a gene on a chromosome.

Denaturation
The loss of the native 3-D structure of a molecule.

Denature
To cause a protein to fold into a structure other than the native 3-D conformation; to convert double-stranded DNA to single-stranded DNA.

Dendrimer
A branching polymer. Dendrimers are used to transfer genetic material into living cells.

Dendrite
A branching process of a neuron that transmits impulses to the body of the neuron.

Dendritic cell
A cell found in lymphoid organs and non-lymphoid tissues that presents antigens to T- lymphocytes.

Dendrogram
A tree-form diagram that is a graphic depiction of hierarchical relationships between sequences or organisms.

Deoxyadenosine
A nucleoside form of adenine.

Deoxycytidine
A nucleoside form of cytosine.

Deoxyguanosine
A nucleoside form of guanine.

Deoxyribonuclease (DNase)
An enzyme that catalyzes the cleavage of DNA.

Deoxyribonucleic acid (DNA)
A long macromolecule with a duplex structure composed of complementary deoxyribonucleotide strands of opposed polarity.

Deproteinization
The removal of protein from a sample.

Detergent
An agent that reduces the surface tension of a liquid. Detergents are often used to solubilize proteins.

Diabetes
A disease caused by loss of control of glucose homeostasis.

Dibasic cleavage site
A site within proteins specifically recognized and cleaved by endopeptidases.

Dictyostelium discoideum (D. discoideum)
A single-celled ameoba that is a model organism for studies of chemical signaling and chemotaxis.

Dideoxy sequencing
A chain-termination method for sequencing DNA that utilizes dideoxynucleotides.

Differential display
A technique for determining differences in gene expression under two different conditions or between two tissues.

Differential splicing
The process by which many mRNAs may be generated by selectively joining RNA sequence modules (exons) within a single primary RNA.

Differentiation
The acquisition of specialized structural and functional features by unspecialized cells.

Diffraction
The bending of light caused by the presence of an object.

Digestion
The hydrolysis of macromolecules resulting in the release of component structures.

Dilution quenching
The reduction of the luminescence of a sample by dilution.

Dimer
Two reversibly associated macromolecular structures; two covalently associated molecules.

Dipeptide
A two-residue peptide.

Diploid
A cell or nucleus that has two sets of homologous chromosomes, one derived from each parent.

Directed molecular evolution
A protein engineering technique that uses genetic algorithms to evolve molecules with new functions.

Discontinuous epitope
An antigenic determinant created from discontinuous protein segments associated in 3-D space by folding.

Discovery-driven research
Exploratory research that begins with the description of complex networks of interactions within an entire genome.

Displacement loop (D-loop)
The structure formed when a third strand of DNA is taken up by double-stranded DNA.

Dissociation constant (Kd)
Tendency of a complex to dissociate. The smaller the Kd, the less likely is dissociation.

Disulphide bond
A covalent bond between the sulfur atoms of two cysteines within the same protein or in two different proteins.

Divergence
Evolutionary process that increases differences in initially similar organisms.

DNA duplex
The structure of double-stranded DNA consisting of two polynucleotide chains of opposed polarity linked by hydrogen bonds between complementary base pairs.

DNA fingerprinting
The generation of a unique DNA pattern that is a genetic profile for an individual.

DNA fragmentation
The endonucleolytic cleavage of genomic DNA at internucleosomal sites. DNA fragmentation occurs during apoptosis.

DNA glycosylase
Enzymes that initiate DNA repair by hydrolyzing links to bases.

DNA gyrase
A name for DNA topoisomerase.

DNA helicase
An enzyme that catalyzes the unwinding of the DNA helix.

DNA ladder
A set of synthetic DNA fragments that differ in length.

DNA ligase
An enzyme that catalyzes the joining of DNA strands.

DNA linker
An oligonucleotide containing a sequence that forms a restriction site in the presence of complementary sequence.

DNA melting temperature
The temperature at which DNA undergoes a transition from helix to coil structure.

DNA methylase
An enzyme that catalyzes the addition of methyl groups to DNA.

DNA methylation
The inactivation of genes by the addition of methyl (-CH3) groups to cytosine.

DNA polymerase
An enzyme that catalyzes the synthesis of deoxyribonucleotides into a sequence complementary to a pre-existent DNA or RNA template.

DNA primase
A DNA-directed RNA polymerase that synthesizes short RNA primers during DNA replication.

DNA sequencing
The determination of DNA base sequence order.

DNA topoisomerase
An enzyme that changes the superhelix density of supercoiled DNA.

DNA vaccine
A DNA construct that is introduced into cells and subsequently translated into immunogenic proteins.

DNase footprinting
A technique for locating the DNA sites bound by proteins that is based on the resistance of protein-DNA complexes to the action of nucleases.

Docking
Computational exploration of the possible binding modes of a ligand to an enzyme, receptor, or DNA.

Docking protein
A synonym for signal recognition particle receptor.

Domain
A compact structural region within a protein with a distinct function.

Dominant allele
An allele with a phenotype that is expressed whether the allele is heterozygous or homozygous.

Downstream
In the direction of the 3' end of a DNA strand.

Drosophila melanogaster (D. melanogaster)
A fruit fly used as a model organism for genetic studies.

Drug
A molecule used to diagnose, treat, mitigate, or prevent disease.

Drug delivery
The delivery of a drug to the site of action. The pharmaceutical formulation may target the molecule for transdermal, oral, or nasal/pulmonary delivery. Liposomes deliver molecules through membranes and immunotoxins target antibodies to specific tissues.

Drug discovery
Processes for the the identification and development of drugs. High-throughput methods that utilize combinatorial chemistry, genomics, and proteomics information are the starting point. Additional research to characterize lead compounds is followed by clinical trials.

dsDNA
Double-stranded DNA.

Duplex
A molecular structure consisting of two strands of opposed polarity.

Dysplasia
An early stage of carcinogenesis characterized by changes in epithelial morphology.

ETop
E. coli, escherichia coli
A bacterium used extensively for research.

Ecotropic
A retrovirus that can replicate only in the host of the species in which it originated.

Ectoderm
The outer of the three embryonic germ layers. The ectoderm gives rise to the neural tissue and epidermis.

Ectopic
Occuring in an unusual place or form.

Edible vaccine
A vaccine based on the engineered expression of an antigenic protein by an edible plant. Following consumption, the protein is recognized by the immune system.

Editing
Altering a nucleic acid sequence so as to preserve accuracy of information transfer.

Editosome
The complex that edits RNA transcripts.

Effector
A small molecule that binds a protein in a regulatory manner.

Electrocompetent cells
Cells optimized for the introduction of DNA by electroporation.

Electroelution
The transfer of biomolecules from an electrophoresis gel to a membrane surface.

Electron density map
A 3-D representation of the electron density of a molecular structure based on x-ray diffraction data. The map is calculated using a Fourier synthesis, a summation of waves of known frequency, amplitude, and phase.

Electronic lysis
Bacterial lysis due to electronic pulses.

Electroosmosis, electroendosmosis
The movement of a liquid through a material following the application of an electric field.

Electrophoresis
The movement of charged particles through a fluid following the application of an electric field.

Electroporation
The generation of transient pores in the membrane of living cells by exposing them to brief electrical impulses. Electroporation is used to introduce DNA into cells.

Electrospray
A method for generating a fine spray of highly charged droplets.

Electrospray ionization-mass spectrometry (ESI-MS)
A method for the solution ionization and mass analysis of macromolecules and small polar molecules.

Electrotaxis
The movement of organisms in response to an electric field.

Embryo
The structure that develops from the zygote.

Embryonic stem cell (ESC)
A totipotent cell cultured from an early-stage embryo. Genetic modification of embryonic stem cells produces transgenic animals.

Emergent
Describes a property of a system that is not predictable from the starting conditions.

Enantiomer
One of the two stereoisomers of a chiral compound. One enantiomer of a chiral drug may be the basis of the therapeutic effect.

Enantiopure
Consisting entirely of one stereoisomer of an enantiomeric compound.

Encapsulation
A method for immobilizing cells for use in a bioreactor, usually based on the use of polysaccharides or collagen to coat cells. Also, cell encapsulation is used in tissue engineering.

End group analysis
The determination of the terminal residues of a nucleic acid or protein.

Endergonic
An energy-requiring reaction.

Endocrine
A gland that synthesizes and secretes hormones directly into the circulatory system.

Endocytosis
The uptake of extracellular materials by a cell.

Endoderm
The inner germ layer that gives rise to the internal tissues.

Endogenous
Developed from within a cell, tissue, or organism.

Endonuclease
A nuclease that cleaves nucleic acids at specific internal sites.

Endopeptidase, endoprotease
A protease that cleaves peptides and proteins at internal sites.

Endophyte
A microorganism living within plant vascular tissue.

Endoplasmic reticulum (ER)
A membrane system that ramifies throughout the cytoplasm and is involved in the synthesis, processing, transport, and secretion of proteins.

Endosome
Organelle containing material ingested by endocytosis.

Endotoxin
Microbial toxin, such as a cell-surface polysaccharide, that is not easily separated from the cell.

Energy transfer
The transfer of energy from one chromophore to another by a process dependent on the distance between the two molecules. Techniques based on energy transfer are useful for structure studies that depend on proximity of two groups.

Energy trapping
The capture of energy released in one reaction for use in a second reaction.

Enhancer
DNA sequence that is bound by regulatory proteins that enhance the rate of transcription of a gene that may be thousands of base pairs distal to the enhancer sequence.

Envelope
A lipoprotein outer layer of enveloped viruses that is derived from the plasma membrane of the host cell.

Envelope protein
A protein or glycoprotein component of the viral envelope.

Enzyme
A protein that catalyzes biochemical reactions. Substrates are bound and oriented within the active site of the enzyme in a manner that facilitates the formation of the transition state and the conversion to products.

Enzyme denaturation
The loss of the 3-D structure of an enzyme.

Enzyme electrode
An enzyme-linked electrode that senses a substrate or product of the reaction catalyzed by the enzyme.

Enzyme induction
The synthesis of an enzyme at a greatly increased rate in the presence of an inducer.

Enzyme linked immunosorbent assay (ELISA)
An assay based on the use of an enzyme to catalyze a reaction that generates a product detectable by colorimetric methods. The enzyme is conjugated to an antibody that is specific for the antigen to be detected.

Enzyme stabilization
The stabilization of the active structure of an enzyme by binding with antibodies. The binding of monoclonal antibodies targeted to regions other than the active site increases the half-life of the enzyme many times.

Eosinophil
A polynucleated granulocyte containing granules filled with hydrolytic enzymes.

Epigenetic
Mechanisms controlling gene expression and interaction during development that do not depend on changes in DNA sequence.

Epigenomics
The genome-wide study of the distribution of methylated and unmethylated nucleoside residues within the genome.

Epigenotype
A phenotype derived by mapping epigenetic parameters, such as DNA methylation.

Epimer
One of two stereoisomers that differ in configuration at one chiral center.

Epimerase
An enzyme that interconverts epimers.

Episome
An extrachromosomal DNA fragment, such as a plasmid.

Epistasis
The blocking of the effects of one gene by the expression of another, non-allelic gene.

Epithelium
A sheet of cells above the basal lamina that is specialized for protection or transport.

Epitope
The antibody-binding region of an antigenic molecule.

Epstein-Barr virus
A herpes virus that causes mononucleosis.

Equilibrium
A state of balance in which there is no net change.

Equilibrium constant (K)
An expression of chemical equilibrium under defined conditions. K is defined as the ratio of the forward and reverse rate constants for a chemical reaction. At equilibrium K equals the product of the reactant concentrations divided by the product of the reactants.

Erythropoiesis
The production of erythrocytes (red blood cells) in the marrow of adults from pluripotent stem cells.

Erythropoietin
A cytokine that stimulates differention of bone marrow stem cells, accelerates cell maturation, and maintains the level of circulating erythrocytes.

Essential
Required for the normal growth of an organism but not synthesized by the organism.

Essential amino acid
An amino acid that cannot be synthesized by a cell or organism and must be supplied as a nutrient.

Essential fatty acid
A polyunsaturated fatty acid that cannot be synthesized by a cell or organism and must be supplied as a nutrient.

Established cell line
Cultured cells that may be subcultured indefinitely.

Etiology
Study of the cause of and progression of disease.

Euchromatin
The highly dispersed region of chromatin present during interphase. Euchromatin corresponds to regions of the chomosomes containing actively transcribed genes.

Eukaryote
Any cell that contain a nucleus, including protists, animals, fungi, and plants. Eukaryotes are characterized by internal membrane systems that partition them into functional zones, such as the nucleus, mitochondria, and endoplasmic reticulum, and cytoskeletal structures that control cell form.

Evolution
The process of cumulative change occurring over successive generations.

Ex vivo
The external alteration of tissue taken from an organism and subsequently returned to the organism.

Exa-
A prefix indicating 1018; a quintillion.

Excimer
An adduct between a molecule that has been excited by a photon and a second molecule.

Excinuclease
An excision nuclease involved in DNA repair.

Excision repair
A mechanism for the repair of DNA damage.

Excite
To raise a molecule from the ground state to the excited state.

Exergonic
A reaction that releases energy.

Exocrine
A gland that utilizes a duct for the secretion of molecules.

Exocytosis
The secretion or release of intracellular materials to the extracellular space.

Exogenous
Originating outside a cell, tissue, or organism.

Exon
The protein coding sequence of a eukaryotic gene. Exons are separated from introns by splice junction sequences.

Exon mapping
The identification of the exons within a gene using hybridization to cDNA.

Exon shuffling
The recombination of exons by strand crossover.

Exonuclease
A nuclease that catalyzes sequential cleavage of nucleotides from the 5' or 3' end of a polynucleotide chain.

Exopeptidase
A peptide hydrolase that cleaves amino acid residues from the N- or C-terminus of a peptide or protein.

Exoribonuclease
A ribonuclease that catalyzes sequential cleavage of nucleotides from the 5' or 3' end of a ribonucleotide chain.

Exotoxin
A toxin released by a microbe.

Expressed sequence tag (EST)
A partial sequence of an expressed gene. EST sequence is obtained by high- throughput methods and is useful in the mapping of genomes.

Expression
The transcription and translation of a gene. Microarrays are used to detect patterns of gene transcription in different tissues during development, and in response to a stimulus or disease. Protein chips make possible the analysis of protein levels.

Expression profiling
A high-throughput method for evaluating the degree and timing of gene expression in a cell or tissue.

Expression system
A cell-based protein synthesis system programmed by an expression vector.

Expression vector
Plasmid or virus vector that carries into a cell a DNA sequence that directs the synthesis of a protein.

Extein
A protein-splicing product formed after the excision of an intein.

Extensible markup language (XML)
A set of specifications for formatting web documents that allows the creation of custom data tags that enable flexible transmission of data between applications and servers.

Extracellular matrix (ECM)
A complex mixture of polysaccharides (glycosaminoglycans or cellulose) and proteins (collagen) secreted by cells. The extracellular matrix serves as a structural element in tissues.

Extrachromosomal
External to the chromosome.

Extremophile
An organism that grows optimally in extreme conditions, including extreme temperature, pressure, pH, ionic concentration, and pressure.

Extremozyme
An enzyme from an extremophile.

 FTop
F factor (fertility factor)
An episomal genetic element that enables a bacterium to transfer extrachromosomal DNA to a second bacterium.

F(ab)2 fragment
A disulfide-bonded immunoglobulin fragment obtained by papain digestion that contains both antigen binding sites.

Fab fragment
An immunoglobulin fragment obtained by papain digestion that contains a single-antigen binding site.

Facultative anaerobe
An organism that grows in the presence or the absence of oxygen.

False negative
A test result that wrongly shows an effect to be absent.

False positive
A test result that wrongly shows an effect to be present.

FASTA
An algorithm for identifying sequence similarities.

Fatty acid
A long-chain aliphatic acid that is found in natural fats.

Fc fragment
The immunoglobulin fragment obtained by papain digestion that contains the complement binding site.

Fc receptor
A protein that binds the Fc region of an immunoglobulin.

Femtomole
One quadrillionth mole; 1015.

Ferrobacteria
Bacteria that utilize iron as an energy source.

Fetal antigen
An embryonic antigen that may be re-expressed in cancer.

Fiber-optic microarray
A microarray based on the attachment of DNA samples or beads to the micro-scale wells at the distal end of an optical fiber bundle.

Fibroblast
An epithelial cell precursor.

Fibrous protein
A protein that aggregates to form filaments and functions as a structural protein.

Fidelity
The degree to which output reflects input. The extent to which transcripion, translation, and replication represent template information.

Fingerprint
Any technique that enables the identification of substances by the comparison of patterns. Examples include DNA, protein, peptide, and chemical fingerprinting.

First principle molecular dynamics
The use of quantum chemical interactions to simulate the motion of molecules.

Flow cytometry
The analysis and sorting of cells that have been reacted with fluorescent probes. The sorting process is based on detection of fluorescence emitted by single cells within droplets.

Flow field effect (flowFET)
A technology utilized in the design of microfluidics systems that utilizes field effects to control flow.

Fluorescein
Dye that fluoresces green when exposed to blue or ultraviolet light.

Fluorescence
The emission of electromagnetic radiation following absorption of shorter wave length light.

Fluorescence activated cell sorter (FACS)
A system for sorting cells by flow cytometry, a method based on the analysis and sorting of cells that have been reacted with fluorescent probes. The sorting process is based on detection of fluorescence emitted by single cells within droplets.

Fluorescence energy transfer
Transfer of energy between two fluorophors.

Fluorescence enhancement
The enhancement of fluorescence by the polarity of the medium.

Fluorescence immunoassay (FIA)
An assay technique based on a fluorescent-labeled antigen.

Fluorescence in situ hybridization (FISH)
The use of fluorescent probes that emit light of different colors to tag DNA probes that hybridize specific chromosomal regions.

Fluorescence polarization
The partial polarization of light emitted from fluorescent molecules.

Fluorescence probe
Molecules that change in fluorescence upon interacting with another structure.

Fluorescence resonance energy transfer (FRET)
A technique useful for analyzing intermolecular distances based on the transfer of energy from a donor molecule to an acceptor molecule without the emission of a photon.

Fluorescent protein
An autofluorescent protein that is used as a reporter molecule, for example, green fluorescent protein (GFP).

Fluorophor
A fluorescent molecule or group.

Folding
The acquisition of 3-D structure by a protein; the pattern of the 3-D structure that is the result of the folding process.

Frameshift mutation
The addition or deletion of a nucleotide to a DNA sequence, causing out-of-phase translation.

Frameshift suppressor
A mutation that suppresses a frameshift mutation by correcting the phase of translation.

Functional complementation (genetic complementation)
The restoration of function by the introduction of exogenous DNA.

Functional genomics
The large-scale exploration of gene function that includes the analysis of regulatory networks, biochemical pathways, protein-protein interactions, the effects of gene knockouts, and the results of functional complementation of knockouts.

Functional group
A group within a molecule that confers characteristic properties.

Functional proteomics
The large-scale study of protein function, especially protein-protein interaction networks, biochemical pathways, and post-translational modifications.

Fusion protein
The expressed protein resulting from the fusion of two genes.

Fusogen
A substance that induces membrane fusion.

Futile cycle
A metabolic cycle that converts energy to heat.

GTop
G protein, GTP binding protein
A heterotrimeric guanine nucleotide binding protein that transduces a signal derived from a transmembrane receptor; also, small cytoplasmic proteins that regulate intracellular process.

Gamete
Mature reproductive cell with a haploid set of chromosomes.

Gap
A space introduced into a sequence within a multiple sequence alignment that allows similar or conserved sequence regions to be aligned in columns.

Gap junction
A specialized area of apposed plasma membranes containing connexons, proteins that bridge the extracellular space and that allow the cytoplasm of one cell to communicate with that of the other cell.

Gap penalty
A penalty subtracted from a sequence alignment score due to the introduction of a gap or the elongation of a gap.

Gap phase
G1 and G2 phases in cell division, during which there is no DNA synthesis.

Gap repair
The repair of a gap (or nick) introduced into a DNA strand by the loss of one or more nucleotides.

Gated channel
An ion channel that allows ion entry under specific conditions.

Gated ion channel
A transmembrane protein that allows ion fluxes to pass under defined conditions. Voltage-gated channels respond to the transmembrane potential difference, and ligand-gated channels to the presence of specific neurotransmitters.

Gel electrophoresis
A technique for the separation of nucleic acids or proteins based on the movement of molecules through a gel matrix under the influence of an applied electrical field.

Gel retardation assay (gel shift assay, electrophoretic shift assay)
A gel electrophoresis technique that detects DNA sequences that bind proteins.

Gene
A DNA region that corresponds to a single protein, a set of alternately spliced protein isoforms, or an RNA. The sequence of a gene consists of the entire functional unit and includes noncoding regulatory sequences and introns, as well as coding regions.

Gene amplification
Increased replication of a gene.

Gene chip
A gene expression microarray.

Gene dosage
The number of times a gene occurs within a genome.

Gene duplication
The duplication of DNA sequences corresponding to genes.

Gene expression
The conversion of DNA sequence information to a phenotype. Gene expression involves activation of transcription, processing of the transcript, translation of structural genes, and assembly of the protein products.

Gene expression markup language (GEML)
An Extensible Markup Language (XML) tag set that provides a standard method for exchanging gene expression data and annotation.

Gene frequency
A measure of the occurrence of an allele in a population.

Gene gun
A device used for the high-velocity injection of DNA-coated particles directly into tissues, cells, or organelles.

Gene marker
A DNA segment or phenotypic trait that serves as a marker for a gene.

Gene pool
The sum of genetic information for a population.

Gene product
The protein or RNA encoded by a gene. A single gene may have multiple protein products, due to extensive post-translational modification. The large-scale study of all possible gene products is the goal of the Human Proteome Project (HUPO).

Gene redundancy
Multiple copies of a single gene.

Gene symbol
The acronym or abbreviation corresponding to a given gene name. Genes and markers may have multiple symbols and names due to rediscovery or correlation to function following discovery.

Gene synthesis
The synthesis of an entire gene by hybridizing oligonucleotides, which are subsequently joined enzymatically.

Gene targeting
The inactivation of a specific gene.

Gene therapy
The delivery of genes to cells in order to correct genetic mutations associated with hereditary disease, to stimulate the immune system, or to target a tumor for subsequent drug therapy.

Generation time
The time interval between successive cell divisions.

Genetic algorithm
An algorithm for optimizing a property based on an evolutionary mechanism that uses replication, deletion, and mutation processes carried out over many generations.

Genetic banking
The deposit of an individual's genetic information to a database that enables the individual to control access.

Genetic code
The code by which a nucleotide sequence is translated into an amino acid sequence. Each three nucleotide triplet constitutes a codon; the 64 codons correspond to 20 amino acids and to signals for the initiation and termination of transcription.

Genetic complementation (functional complementation)
The restoration of function by the introduction of exogenous DNA.

Genetic drift
A change of gene frequencies within a population over time.

Genetic fingerprinting
Analyzing gene expression patterns using computational techniques, such as artificial neural networks.

Genetic map
A map of relative chromosomal locations based on recombination data.

Genetic marker
An observable characteristic useful for genetic analysis.

Genetic polymorphism
The presence of two genotypes in a population.

Genetic recombination
The exchange of genetic material between homologous chromosomes in meiosis.

Genetic screening
Testing of individuals for a gene or metabolite.

Genetic variation
Genetic heterogeneity in a population.

Genetics
The biology of heredity and variation.

Genome
The total genetic information of an organism.

Genome map
The linear arrangement of genes and markers within the chromosomes of a genome.

Genomic epidemiology
The genome-wide study of the relation between genetic variation and disease.

Genomic library
A set of clones consisting of ramdomly generated overlapping DNA fragments representing the entire genome of an organism.

Genomics
The large-scale investigation of the structure and function of genes. Understanding the structure and function of genomes aids in drug discovery and development, agroscience research, and other fields.

Genotype
The genetic information for an organism that is carried on the chromosomes and extrachromosomally.

GERL
A region of the endoplasmic reticulum involved in the packaging of molecules. The GERL includes the Golgi, smooth endoplasmic reticulum, and lysosomes.

Germ cell
Any cell of the germ line. Germ cells are the reproductive cells and include the egg and sperm cells.

Germ line
A cell line that gives rise to gametes.

Germ line mutation
A heritable genetic change in the germ line cells.

Giberrellin
A plant hormone that regulates growth.

Glial cell
A specialized cell that surrounds neurons, providing metabolic and physical support.

Glioblastoma
A malignant brain tumor of glial origin.

Glioma
A non-metastatic brain tumor of glial origin.

Global alignment
A sequence alignment over the entire length of two nucleic acid or protein sequences.

Globular protein
A protein that is rounded in shape.

Glycan
A polysaccharide consisting of monosaccharides joined by glycosidic linkages.

Glycation
A non-enzymatic reaction that adds a carbohydrate group to a protein or peptide.

Glycobiology
The biochemistry of glycoconjugates.

Glycocalyx
A cell coating consisting of glycoproteins and proteoglycans.

Glycoconjugate
A complex carbohydrate attached to a lipid, peptide, or protein.

Glycoform
A glycoprotein variant that differs in the oligosaccharide moiety.

Glycolipid
A molecule consisting of a short carbohydrate chain attached to a lipid.

Glycome
The total carbohydrate complement of a cell.

Glycopeptide
A protein with covently bound carbohydrates.

Glycophorin
A carbohydrate-bearing transmembrane protein found on the surface of erythrocytes.

Glycoprotein (gp)
A protein with covalently bound carbohydrates.

Glycoprotein remodeling
The removal of oligosaccharides from a glycoprotein by a glycosidase.

Glycosaminoglycan
A polysaccharide containing aminomonosaccharide residues.

Glycosidase
An enzyme that hydrolyzes glycosidic bonds between monosaccharide components of a polysaccharide.

Glycoside
A compound in which a glycosyl group has been substituted for a hydroxyl group.

Glycosylation
The post-translational addition of carbohydrate groups to a molecule. Glycosylation of proteins occurs via the amide group within the sequence Asn-X-Ser/Thr (or through the hydroxyl of the serine or threonine residue in the sequence).

Gnotobiotic
A system to which only preselected components, organisms and nutrients are introduced.

Golgi body, Golgi apparatus
Intracellular stack of vesicles in which glycosylation and packaging of proteins and peptides destined to be secreted takes place. Proteins are processed as they progress from the cis- to the trans-Golgi region.

Graft-versus-host response (GVH)
A reaction that occurs when lymphocytes of a different MHC class are introduced into a host, resulting in the reaction of the lymphocytes against the host.

Granularity
The degree to which a system contains separate components. Systems with greater granularity are more flexible.

Granulocyte
A white blood cell containing large granules.

Granulocyte-colony stimulating factor (G-CSF)
A cytokine that controls the differentiation of granulocytes and macrophages.

Growth factor
A substance that promotes the growth of cells. Growth factors include epidermal growth factor (EGF), fibroblast growth factor (FGF), erythropoietin (EPO), hematopoietic cell growth factor (HCGF), platelet-derived growth factor (PDGF), stem cell factors, and neurotrophins.

Guanine
A purine that is one of the five main bases found in nucleic acids. Guanine base pairs with cytosine.

Guanosine
A nucleoside form of guanine.

Guide RNA (gRNA)
A small RNA involved in a specialized form of RNA editing.

HTop
Hairpin
A structure in which adjacent segments of DNA or RNA fold together and are stabilized by base pairing, creating a loop of single-strand DNA or RNA.

Hairy root culture
A plant culture system based on highly branched roots generated by plant tissue with agrobacterium rhizogenes. The hairy root cultures grow on simple media and produce secondary metabolites at normal levels.

Half-life
The time that it takes for half of the activity of a molecule to decay.

Halophile
A microorganism that grows optimally in a highly saline environment.

Haploid
Genetic material consisting of a single chromosome set (half of the diploid number). Egg and sperm cells of animals and egg and pollen cells of plants are haploid.

Haplotype
A set of genes on a single chromosome.

Hapten
A small molecule that is not immunogenic unless attached to a carrier protein.

Hardy-Weinberg Law
A mathematical statement of the concept that gene and genotype frequencies are constant from generation to generation in a large, interbreeding population with random mating in the absence of selection, mutation, or migration.

Heat shock protein
A protein synthesized in response to cellular stress, including high temperature. Heat shock proteins function as molecular chaperones to protect proteins from premature folding.

Heavy chain
The heavier of the two types of immunoglogulin chains.

Helicase
A protein that unwinds the DNA double helix during replication.

Helix breaker
An amino acid residue that interrupts alpha helical structure.

Helix destabilizing protein
A protein that binds single-stranded DNA.

Helix former
An amino acid residue that favors the formation of alpha helix.

Helix loop helix (Helix turn helix)
A structure characteristic of DNA-binding proteins.

Helix-to-coil transition
The transition of a nucleic acid or protein from the native to the denatured state.

Helper cell
A T-lymphocyte that binds antigens on the surface of presenting cells and secretes lymphokines that activate cytotoxic cells.

Helper virus
A virus that provides functions missing in a defective virus.

Hematologic growth factor
A colony stimulating factor that stimulates the production of some types of white and red blood cells.

Hematopoesis
The proliferation and differentiation of stem cells to produce blood cells. Hematopoeisis occurs in the bone marrow in adults.

Heme
An iron-porphyrin compound that occurs as a prosthetic group in hemoproteins.

Hemoprotein
A protein bound to an iron-porphyrin compounds such as hemoglobin, myoglobin, and members of the cytochrome group.

Heparan
A glycosaminoglycan.

Hepatocarcinoma
A cancer of the liver that is derived from hepatocytes.

Hepatocyte
An epithelial cell of the liver responsible for the synthesis, degradation, and storage of a variety of materials.

Herpes virus
A virus group that includes the Epstein-Barr Virus and Herpes Simplex.

Heterochromatin
The highly condensed region of chromatin present during interphase. Chromosomes in this region are transcriptionally inactive.

Heterodimer
A dimer composed of two different molecules.

Heteroduplex
A double-stranded DNA in which the base sequences are not completely complementary due to recombination or mutation.

Heterogeneous RNA (hnRNA)
A mixture of different molecular weight RNAs synthesized by RNA polymerase II.

Heterogeneous RNP (hnRNP)
The complex of heterogeneous nuclear RNA with proteins.

Heterokaryon
A cell with more than one nucleus.

Heterologous
Consisting of different elements.

Heterozygosity
The presence of different alleles on homologous chromosomes.

Heterozygote
An organism with different alleles on homologous chromosomes.

Heuristic
A method based on empirical information that has no explicit rationalization.

Heuristic algorithm
A programming strategy based on trial-and-error methods and feedback evaluation.

Hidden Markov Model
A probabilistic model used to align and analyze sequence datasets by generalization from a sequence profile.

High field NMR
A high-resolution NMR method based on higher field magnets that enables the analysis of large molecules.

High-content screening
Simultaneous multiparametric analysis of complex systems, such as living cells.

High-throughput system, High-throughput screening (HTS)
A massively parallel screening technique for the simultaneous assay and evaluation of large numbers of samples.

Hinge region
A proline-rich region that allows an antibody to flex upon binding antigen.

Histocompatibility
The ability of a host to tolerate a tissue graft.

Histocompatibility antigen
A genetically determined antigen that determines the immune response to grafts.

Histogram
A graphic representation of a frequency distribution.

Histone
Abundant small protein rich in arginine and lysine that associates with DNA and enables the packaging of DNA into chromosomes.

HLA
Abbreviation for human leukocyte-associated antigen.

Hollow fiber
Refers to systems based on hollow semi-permeable fibers that are used for protein separation and cell culture. Hollow-fiber bioreactors are used to maintain mammalian cells in culture, particularly cells producing monoclonal antibodies.

Holoenzyme
A catalytically active enzyme that includes cofactors.

Homeobox
A highly conserved nucleotide sequence that is important to the orchestration of gene expression during development.

Homeodomain
A protein motif encoded by DNA sequence within the homeobox.

Homeotic gene
A homeobox- or homeodomain-encoding gene.

Homodimer
A dimer composed of identical molecules.

Homologuous recombination
Exchange of sequence information between two homologous DNA molecules. Homologous recombination contributes to DNA repair and is essential for maintaining genome stability.

Homozygosity
The presence of identical alleles on homologous chromosomes.

Homozygote
An organism with identical alleles on homologous chromosomes.

Horizontal study
The study of a population at a point in time. Horizontal studies are also known as cross-sectional studies.

Hormone
A substance formed in a specialized gland or group of cells that has regulatory effects on another gland or group of cells. Hormones are usually transported in the circulation.

Host
A cell used for the reproduction of foreign DNA, such as a plasmid or virus.

Host-vector system
A system for the propagation of a DNA vector in a host cell.

Housekeeping gene
A constitutively expressed gene. Housekeeping genes are continuously transcribed at low basal levels.

Human immunodeficiency virus (HIV)
The retrovirus that causes AIDS, acquired immune deficiency syndrome.

Humoral
Contained in a bodily fluid.

Humoral immunity
Immunity mediated by humoral antibodies.

Hybrid antibody
An immunoglobulin produced by fusing hybridomas producing two different antibodies, resulting in the production of a third, heterophile antibody.

Hybrid cell
A cell formed by fusion of two cells. Hybrid antibodies may also be produced by combining two antibodies.

Hybridization
The annealing of two complementary nucleic acid strands to form a double-stranded molecule; a technique for detecting specific nucleic acid sequences.

Hybridoma
A permanent cell line generated by cell fusion that secretes a specific monoclonal antibody.

Hydrolysis
The rupture of a chemical bond by a reaction that involves water.

Hydrophilic molecule
A polar compound that forms hydrogen bonds with water and dissolves easily in water.

Hydrophobic molecule
A nonpolar compound that does not form favorable binding interactions with water, and is insoluble in water.

Hyperplasia
An increase in tissue due to enhanced cell division. Hyperplasia may be reversed by removal of the stimulus.

Hypersensitivity
An excessive immune response that results from previous exposure to an antigen. Immediate responses are antibody-mediated and occur in minutes; delayed responses are mediated by T-cells and occur about 24 hrs later.

ITop
Idiotope
An antigenic determinant within the variable region of an antibody.

Idiotype
The antigenic specificity defined by the idiotopes within the antigen combining site of an antibody.

Imaging agent
A chemical that is readily detectable by a medical imaging system. Imaging agents include electron-opaque molecules, such as gold particles, radioisotopes, such as technetium, and stable isotope-labeled molecules.

Immobilized cell biosensor
A biosensor that uses living cells as the detection system. The cell signal is read out by a system that produces fluorescence, or by direct electrochemical coupling.

Immortalization
The generation of cells that undergo an infinite number of division cycles. Immortalization of cells may be brought about by transfection with oncogenes, transfection with telomerase reverse transcriptase, induction by mutagens, or may be spontaneous.

Immune complex disease
A disorder characterized by the presence of immune complexes in bodily fluids.

Immune deficiency disease
A disorder characterized by the suppression of the immune reaction.

Immune response
The total immunological reaction of an organism. The immune response includes antibody production, cell-mediated immunity, and complement activation.

Immunoassay, immunodiagnostic
An antibody-based technique for the qualitative and quantitative characterization of samples. Different antibody labels and imaging agents used to detect antibody-antigen interactions distinguish the different assay types: ELISA (enzyme-linked immunosorbent assay) uses an enzyme that produces a colorimetric product, RIA (radioimmunoassay) uses a radioactive label, FIA (fluorescent immunoassay) uses a fluorescent molecule, CLIA (chemiluminescent immunoassay) uses a light-generator.

Immunoconjugate
An antibody conjugated to a molecule, such as a fluorescent label or an enzyme, that produces a colorimetric product.

Immunogen
A molecule, molecular assembly, or organism that is specifically recognized by an antibody; an antigen.

Immunogenic
Capable of stimulating an immune response.

Immunoglobulin
A protein produced by lymphocytes that consist of two heavy chains, two light chains, and an oligosaccharide moiety.

Immunomodulation
Activation or suppression of the immune response.

Immunophenotyping
The typing of cells with antibody markers.

Immunoprecipitate
The precipitate formed in a reaction between an antibody and an antigen.

Immunoprecipitation
The precipitation of a multivalent antigen by a bivalent antibody.

Immunosensor
A microelectronic sensor used on a biochip that senses when a molecule binds to an attached antibody.

Immunosorption, immunoadsorption
The use of antibodies or antigens attached to a solid support to purify antigens or antibodies, respectively, from a mixture.

Immunosuppression
Suppression of the immune response.

Immunotherapeutic
A genetically engineered protein, such as an interferon, interleukin, or a colony-stimulating factor, that enhances the immune response.

Immunotherapy
The use of antibodies, proteins derived from antibodies, or immune cells to treat disease.

Immunotoxin
An antibody joined to a toxic molecule that is used to target toxins to specific tissues.

Imprinting
The differential expression of genes due to differential methylation of nucleosides.

In silico biology
The use of computational algorithms to create virtual systems that emulate molecular pathways, entire cells, or more complex living systems.

In situ hybridization
A technique that uses x-ray film to detect labeled molecules after hybridization of a labeled DNA or RNA probe to DNA or RNA within tissue specimens.

In situ oligonucleotide synthesis
On-chip synthesis of oligonucleotides or peptide nucleic acids.

In vitro
Occurring outside an organism, in culture, or in an extract.

In vivo
Occurring in a living organism.

Inborn error of metabolism
An inherited biochemical variation due to genetic alterations in the genes encoding metabolic enzymes.

Inclusion bodies
Bodies formed within bacterial cells for the storage of various materials. Bacterial systems that express proteins within the cytoplasm form protein-filled inclusion bodies due to the aggregation of misfolded proteins.

Incomplete penetrance
A genotype that is not uniformly expressed as a phenotype.

Inflammation
The immediate defense of tissue against infection or injury.

Information RNA (iRNA)
An RNA sequence that does not encode a protein, but provides regulatory information.

Inhibitor RNA (iRNA)
An RNA that interferes with normal RNA function.

Initiation factor
A protein that promotes the association of ribosomes with mRNA and the initiation of protein synthesis.

Ink-jet technology
A non-contact method for delivering biomolecules to substrate surfaces. Ink-jet technologies rely on piezoelectric propulsion to transfer small molecules to solid surfaces.

Inositol phospholipids
A lipid family characterized by phosphorylated inositol derivatives. Inositol phospholipids are a minor component of the plasma membrane important in signal transduction.

Intein
The internal protein sequence that is excised during protein splicing.

Interferon
A protein liberated by cells following exposure to viruses and other microorganisms. Interferons induce protein synthesis inhibitors that block translation of viral mRNA.

Interleukin
A cytokine that acts as a signal between different leukocyte populations.

Interoperability
Ability of different types of databases, applications, operating systems, and platforms to function in an integrated manner.

Interphase
The stage of a cell not undergoing mitosis or meiosis. Interphase includes G1, S, and G2 phases of the cell division cycle.

Interstitial cell
A connective tissue cell.

Interstitial fluid
Extracellular fluid.

Intradomain
Within a single protein domain.

Intraepithelial
Within an epithelial cell layer.

Intrahepatic
Within the liver.

Intrinsic protein
A transmembrane protein.

Intron
The non-coding (intervening) sequence of a gene that is transcribed into RNA but then excised by splicing to produce an mRNA transcript. Recently eukaryotic nuclear introns have been found to encode proteins.

Invasive
Tending to penetrate healthy tissue.

Inverted repeats
Identical copies of a sequence of double-stranded DNA repeated in inverse order.

Ion
An atom or molecule with a positive or negative electrical charge. Positively charged ions are cations, and negatively charged ions are anions.

Ion channel
Transmembrane protein complex that forms a channel through which specific inorganic ions diffuse.

Ionophore
A small hydrophobic molecule that dissolves in lipid bilayer membranes and increases permeability to inorganic ions.

Ionotropic
A receptor that mediates its effects by regulating ion channels.

Iontophoresis
The transfer of ions across cell membranes due to the application of an electrical potential.

Irreversible inhibitor
A synthetic molecule designed to bind the active site of an enzyme and form a covalent bond with the enzyme.

Ischemia
An inadequate flow of oxygen (hypoxia) due to insufficient blood supply.

Isoantigen
An antigen that elicits an immune response in other individuals of the same species but not in the individual from which the antigen is derived.

Isoelectric focusing (IEF)
An electrophoresis technique based on the movement of proteins through a stable pH gradient established using carrier ampholytes. Isoelectric focusing is the first dimension of 2-D electrophoresis.

Isoelectric point
The pH of a solution in which a protein has no net charge and does not migrate in an electric field.

Isoforms
Multiple related proteins that differ in sequence due to alternate splicing of exons within a single primary RNA transcript or due to derivation from two related genes.

Isoschizomers
Different restriction enzymes that recognize the same sequence, but do not necessarily cut at the same site.

Isotope
A form of an atom that differs from other forms of the atom in atomic weight. Isotopes may be stable (for example, deuterium) or radioactive (for example, tritium). Isotopes are incorporated into tracer molecules used in imaging molecular function in tissues.

Isotypes
Macromolecules with common structural and functional features, such as the IgG, IgM, IgA, IgD, and IgE antibody isotypes.

Isozyme, isoenzyme
One of several forms of an enzyme that differ in primary sequence.

Iteration
A single round of data processing. During iterative data processing, a loop of instructions is executed in a repetitive manner until some threshold is reached.

JTop
Junk DNA
A term used to refer to stretches of DNA within the genome that do not encode genes and are likely to play a structural, regulatory, or undefined role.

 KTop
Kappa (K) chain
One of the two types of light chains that occur in antibodies.

Karyotype
A photomicrograph of size-ordered, banded chromosomes that enables low-resolution physical mapping of features.

Kilobase (kb)
A unit of DNA length; 1 kb is equal to 1,000 base pairs.

Kinetics
The study of the rate of change.

Kinetochore
A pair of structures adjacent to the chromosomal centromere to which spindle microtubules attach.

Klenow fragment
The large fragment of E. coli DNA Polymerase I. The Klenow fragment retains DNA polymerase activity and 3'-5' exonuclease activity, and is used for DNA sequencing.

Knockdown
An alteration of a gene so that it may be expressed conditionally.

Knockin
An alteration of a gene in a way that results in a gain of function.

Knockout
An alteration of a gene that results in loss of function; a transgenic organism in which a gene has been inactivated.

Knowledge mining
The extraction of useful knowledge from data patterns that have been rendered meaningful by the integration of information derived from external sources.

Kozak sequence
A DNA sequence that surrounds the ATG start signal for the translation of an mRNA.

Kringle
A conserved protein domain whose 2-D representation resembles a Scandinavian pastry known as a kringle.

Kuppfer sells
Specialized non-motile macrophages in the liver sinusoidal regions.

LTop 
L-
A configurational prefix that designates one of two chiral configurations (see D-).

Lab-on-a-chip
A microfabricated fluidics system designed to perform high-resolution biochemical analyses.

Lambda bacteriophage
A bacteriophage vector that is widely used as a DNA cloning vector.

Lambda chain
One of two types of light chains that occur in antibodies.

Langmuir-blodgett film
A lipid bilayer on the surface of water.

Laser
A device that emits an intense coherent monochromatic light beam.

Laser capture microdissection
A technique for isolating single cells from tissues. Laser microdissection makes possible the collection of pure populations of cells for the analysis of molecular function.

Laser inactivation
Protein knockout technique based on the binding of a chromophore to a specific protein followed by laser irradiation to inactivate the protein.

Lateral genomics
An approach to genomics that emphasizes lateral gene transfer.

Lead compound
A peptide or small molecule that optimally modulates the activity of a receptor or other target protein. A successful lead compound becomes a drug candidate for further development.

Leader sequence
A short amino acid sequence that determines the localization of a protein within the cell.

Leaving group
A group that departs during a substitution reaction.

Lectin
A glycoprotein that binds sugars and agglutinates cells.

Lentivirus
A retrovirus utilized for gene therapy vectors.

Lepidoptera
Insects such as butterflies and moths.

Leucine zipper
A structural motif characteristic of DNA-binding proteins consisting of a protein dimer formed by two interacting a helices from separate proteins.

Leukemia
A group of neoplastic diseases of leukocytes, often resulting in proliferation of leukocytes.

Ligand
A small molecule that binds to a receptor/protein.

Ligase
An enzyme that ligates (joins) two molecules in an energy-dependent process.

Light chain (L chain)
The shorter of the two protein chains that comprise antibodies.

Linkage
The co-inheritance of two DNA loci that are near each other on the same chromosome.

Linkage map
A map of the relative positions of genetic markers, based on how often they are inherited together.

Lipid
An oil-soluble molecule such as a fatty acid or steroid.

Lipofection
The use of liposomes to transfect cells with DNA.

Lipophilic molecule A
nonpolar compound that readily mixes with lipids or other low polarity substances.

Lipopolysaccharide
A lipid attached to a polysaccharide.

Lipoprotein
A protein conjugated to lipids.

Liposome
A synthetic lipid bilayer vesicle that fuses with the outer cell membrane and is used to transport small molecules into cells.

Lithotroph
A microorganism that synthesizes all organic molecules from inorganic sources.

Live cell array
A micro-system for the high-throughput analysis of intact cells.

Locus (plural, loci)
The specific position of a gene or other chromosomal marker.

Long terminal repeat (LTR)
A long DNA sequence that is repeated at each end of retrotransposon and retrovirus DNA.

Longitudinal study
A study that follows a population forward over time.

Low complexity
A region of protein sequence enriched for a single amino acid.

Luciferase
A mono-oxygenase enzyme that catalyzes bioluminescent reactions. Firefly luciferase used in combination with substrate luciferin is a sensitive assay for ATP.

Luciferin
Any bioluminescent substrate for luciferase.

Lumen
The volume enclosed by the endoplasmic reticulum or the mitochondrial inner membrane; the interior space of a tubular organ such as a blood vessel.

Lumenal protein, luminal protein
A protein that is retained in the rough endoplasmic reticulum due to the presence of a four amino acid signal (KDEL).

Luminophore
A luminescent substance.

Lumisome
A membrane-bound particle isolated from marine organisms that contains proteins that produce luminescence.

Lux proteins
Bioluminescent marine proteins that are the counterpart of the luciferase system.

Lymph node
A small organ that is a component of the lymphatic system and consists of lymphocytes, macrophages, and dendritic cells. The lymph nodes filter lymph from peripheral nodes, and ultimately empty into the thoracic duct.

Lymphocyte
A leukocyte (white blood cell) that functions in specific immunity.

Lymphokine
A factor released by lymphocytes that modulates other cell types.

Lymphoma
A malignant tissue neoplasm that produces a tumor mass, often associated with lymphoid tissue.

Lysis
Cell disintegration due to membrane rupture or the breakdown of the cell wall.

Lysogenic virus
A virus capable of becoming a prophage and integrating into a bacterial genome.

Lysogeny
The ability of a phage to integrate into the bacterial DNA chromosome.

Lysosome
A eukaryotic organelle containing hydrolases active at pH 5. The enzymes break down particles ingested by vacuoles following fusion.

Lysozyme
An enzyme that hydrolyzes glycosidic linkages within peptidoglycans in prokaryote cell walls.

Lytic infection
A viral infection that results in the lysis of the host cell and release of viral progeny.

Lytic virus
A virus that lyses the host cell.

MTop 
M13
A single-stranded bacteriophage vector that is used in the Sanger dideoxy sequencing method.

Macroaggregate
A visible aggregrate of macromolecules.

Macroarray
A low-density “microarray” on a nylon transfer membrane.

Macromolecular crystal
A crystal whose lattice structure is based on macromolecules.

Macromolecule
A molecule larger than about 10 kDA.

Macrophage
A cell characterized by prominent lysosomes and the ability to phagocytose foreign material. Macrophages are involved in both non-specific immunity, due to the phagocytosis of foreign materials, and in specific immunity, due to the presentation of the antigen.

Macrophage-colony stimulating factor (M-CSF)
A growth factor that stimulates macrophage colonies.

Macrorestriction map
A linear map of the order of restriction sites on a chromosome and the distance between sites.

Macroscopic
Visible to the unaided eye.

Magnetic resonance imaging (MRI)
An imaging technique that produces cross-sectional images for medical research. The object to be viewed is exposed to a radio frequency field in the presence of a varying electromagnetic field.

Major histocompatibility antigen, Class I
A cell-surface glycoprotein that enables the immune system to distinguish self; a transplantation antigen.

Major histocompatibility antigen, Class II
A cell-surface glycoprotein found only on the surface of specific lymphocyte cell types and some macrophages.

Major histocompatibility complex (MHC)
The genetic loci that encode the histocompatibility antigens, cell-surface proteins that bind peptide fragments of foreign proteins, present them to T-lymphocytes, and induce an immune response.

MALDI-TOF MS
The abbreviation for Matrix Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry, a high-throughput protein sequencing method based on embedding samples in a matrix from which they are desorbed by laser light.

Malignant
Invasive, capable of metastasis.

Map unit
A unit of genetic length derived from recombination frequency. One map unit corresponds to a recombination frequency of 1%.

Mariculture
The culture of marine organisms.

Marker rescue
The recovery of genetic markers due to recombination events that restore function.

Mass spectrometer (MS)
An instrument that determines the exact mass of charged particles or ions by measuring the flight path through a set of magnetic and electric fields. Mass spectrometers specialized for protein and peptide sequencing are used for high-throughput identification.

Mass spectrometry
A method for identifying molecules based on the detection of the mass-to-charge ratio of ions generated from the molecule by vaporization and electron bombardment. Deflection of the ions through a magnetic field results in a characteristic pattern used to identify the molecule.

Mass-to-charge ratio
The ratio of the mass of an ion being analyzed to its charge.

Massively parallel computing
High-performance computing based on the development of parallel processing algorithms and applications that can be executed simultaneously by many separate processors.

Mast cell
A non-circulating leukocyte characterized by histamine-filled granules. Mast cells are involved in hypersensitivity reactions.

Matrix
A medium in which things are formed, developed, or embedded.

Matrix attachment region (MAR)
A region of a chromosome that binds nuclear matrix proteins.

Megabase (Mb)
A unit of DNA length: 1 Mb equals 1,000,000 base pairs.

Meiosis
Nuclear division that occurs in eukaryotes to produce haploid eggs and spermocytes from a diploid cell. Meiosis consists of two reductive divisions.

Melanocyte
A skin cell that produces and stores the pigment melanin.

Melanophore
A melanocyte with contractile properties that causes the translocation of melanosomes (melanin-containing organelles), resulting in rapid adaptive changes in coloration.

Melting
The thermal denaturation of a macromolecule.

Membrane
A single- or double-layer lipid sheet that separates two compartments.

Membrane channel
Transmembrane protein complex that allows inorganic ions to diffuse passively across the membrane bilayer.

Membrane potential
The electric potential difference across a membrane.

Mendelian inheritance
A hereditary process explainable in terms of the segregation of chromosomes, independent assortment, and homologous exchange.

Mendelian trait
A characteristic that is transmitted according to the laws of genetics formulated by Mendel.

Mesenchymal stem cell (MSC)
A pluripotent cell that differentiates into connective tissue.

Mesenchyme
Embryonic tissue of medodermal orgin that develops into connective tissue, lymphatic tissues, and blood vessels.

Mesoderm
The middle of the three germ layers of an embryo that forms the connective, musculoskeletal, and vascular tissue.

Messenger RNA (mRNA)
The RNA template for protein synthesis. mRNA is formed by transcription of the template DNA strand, followed by the excision of introns and the joining of exons to form mature mRNA.

Meta-analysis
A method for the statistical re-analysis of experimental and correlational results from independent studies that address related research questions.

Metabolic burst, respiratory burst
The response of phagocytes to the uptake of particles that involves the production of hydrogen peroxide, superoxide anions, and hydroxyl radicals.

Metabolic profiling
The measurement of biochemical intermediates within a tissue in order to describe the functioning of metabolic pathways.

Metabolism
Processes for the synthesis, modification, and breakdown of molecules within a living organism.

Metabolite
A molecule synthesized or modified by metabolic processes within an organism.

Metabolome
The total small molecule complement of whole cells.

Metabolon
A supramolecular assembly of sequential metabolic enzymes.

Metabotropic
A receptor that mediates its effects by activating enzymes.

Metacentric
A chromosome with a centromere near the center.

Metadata
Information about data that facilitates access and use of the data.

Metaphase
The stage in mitosis and meiosis during which chromosomes align along the equatorial plane of the cell.

Metastasis
The development of a secondary tumor at a site remote from a primary tumor.

Metazoa
Multicellular animals with a nervous system and tissues.

Micelle
The structure formed by amphipathic molecules in solution that places the polar group toward the solution and the hydrophobic group toward the interior.

Micro chemical system (MiCS)
A miniature system for the synthesis and analysis of chemicals.

Micro total analytical system (µTAS)
A miniature biochemical analysis system based on microsystems technology.

Microarrays
Oligonucleotides, cDNAs, proteins, peptides, or other small molecules organized in a grid on a glass or plastic slide, silicon chip, fiber optic array, or filter membrane.

Microbody
A membrane-bounded cytoplasmic organelle that contains oxidative enzymes.

Microcarrier
Nontoxic, finely particulate material used to grow cells in suspension culture.

Microdissection
Dissection of organisms by mechanically controlled instruments monitored using a microscope.

Microelectromechanical systems (MEMS)
A technology that combines computers with micro-scale sensors, actuators, valves, gears, and mirrors embedded in semiconductor chips.

Microelectronic array
A microarray that uses microelectrodes to concentrate DNA samples and accelerate probe hybrization.

Microfibril
A fibril identifiable only by electron microscopy.

Microfluidics
Lab-on-a-chip technology based on the transport of nanoliter or picoliter volumes of fluids through microchannels within a glass or plastic chip. Microfluidics systems evolved from MEMS research.

Microforge
Device used with a microscope for the generation of micropipets.

Micrograph
The graphic representation of a microscope image.

Microgravity chamber
A rotating wall vessel bioreactor used for tissue engineering that neutralizes gravitational effects on cells. Cells self-associate and grow three-dimensionally to generate tissues.

Microinjection
The injection of a single cell using a micropipet.

Micromanipulator
Instrument used with a microscope for manipulating small instruments and specimens.

Micromodification
Post-translational modification of a protein.

Micron (µ)
A unit of length equal to 10-6 meter.

Microprocessor
An integrated electronic circuit designed to carry out a specific set of operations.

Microreactor
A minitiarized reaction system used for chemical synthesis.

Microsequenator
A device for sequencing small amounts of sample.

Microsome
A small closed vesicle created by mechanical disruption of the rough endoplasmic reticulum.

Microspotting
A contact-based transfer method that utilizes pins or capillaries to deposit biomolecules on a solid surface.

Migration
The movement of a cell over a surface.

Mimetic
A molecule that replicates essential features of another molecule.

Mimotope
A compound that mimics the structure of an epitope and provokes an identical antibody response. Mimotopes are useful in the development of vaccines.

Minichromosome
A plasmid that contains a chromosomal origin of replication.

Minimum recognition unit (MRU)
The complementarity determining region of an antibody.

Minus end
The end of an actin filament to which monomers are added more slowly.

Minus strand
A DNA or RNA strand that is complementary to a viral plus strand.

Mismatch repair
A cell-based enzymatic mechanism that corrects nucleotide insertion errors made during DNA replication by excising the defective sequence and replacing it with the correct sequence.

Missense codon
A codon altered so that it codes for a different amino acid.

Missense mutation
A base substitution that changes a codon into a codon corresponding to a different amino acid.

Mistranslation
The insertion of an amino acid not specified by the corresponding mRNA codon.

Mitochondrial DNA (mtDNA)
Double-stranded DNA contained within mitochondria that encodes mitochondrial tRNAs, rRNAs, and proteins. Several copies of the mitochondrial genome are found in each organelle.

Mitochondrial intermembrane space
The mitochondrial compartment between the outer and the inner membranes.

Mitochondrial matrix
The inner mitochondrial compartment that contains enzymes associated with the oxidation of fatty acids and the tricarboxylic acid cycle.

Mitochondrial RNA
RNA transcribed from mitochondrial DNA.

Mitochondrion (plural, mitochondria)
A self-replicating organelle bound by two bilayer membranes that is found in the cytoplasm of eukaryotic cells. Mitochondria produce ATP via oxidative phosphorylation reactions carried out by respiratory enzymes located in the inner membrane.

Mitogen
A stimulant of cell division.

Mitoplast
The mitochondrial inner membrane and matrix.

Mitoribosome
A mitochondrial ribosome. Mitoribosomes resemble prokaryotic ribosomes rather than the cytoplasmic ribosomes of the cells containing the mitochondria, giving rise to the symbiont hypothesis.

Mitosis
The process of chromosome segregation that occurs during the division of eukaryotic cells. During mitosis, DNA is condensed into visible chromosomes (prophase) that arrange at the cell midplane (metaphase), separate (anaphase), and decondense into the interphase.

Model organism
A relatively simple organism that duplicates some critical aspect of a more complex system that would be difficult to manipulate experimentally. Examples of widely used model systems include Saccharomyces cerevisiae, Caenorhabditis elegans, and Arabidopsis thaliana.

Moiety
A component part of a complex molecule.

Molecular beacon
A single-stranded DNA molecule with a fluorescent reporter group on one end and fluorescence quencher on the other. Unfolding of the self-quenched DNA structure occurs upon hybridization to a complementary sequence and results in the emission of a fluoresence.

Molecular biology
The interpretation of biological events in terms of the physics and chemistry of molecules within cells.

Molecular clock
An evolutionary hypothesis based on the assumption that mutations occur in a regular manner.

Molecular dynamics
The study of intramolecular conformations and molecular motions, using computational simulations.

Molecular electronics
Electronic devices based on components consisting of individual molecules.

Molecular genetics
The study of the molecular structure and function of genes.

Molecular graphics
The computational visualization of macromolecules for the purpose of molecular design, protein engineering, and structural refinement.

Molecular mimics
Chemical compounds that resemble biomolecules and recognize and bind their targets.

Molecular modeling
Computational analysis and modeling of the physicochemical properties of a molecule or biomacromolecule.

Molecular pattern recognition
Computational methods for the analysis of genome-wide expression patterns and and phenotypes.

Molecular replacement
A method for solving biomacromolecular structure based on the use of a model derived from a related, previously solved structure.

Molecular sieve
A material with pores capable of separating molecules on the basis of size.

Monoclonal
Derived from a single clone.

Monoclonal antibody (Mab)
A monospecific immunoglobulin produced by a single clone of cells.

Monocyte
A leukocyte found in bone marrow and in the circulatory system. Monocytes differentiate into macrophages in the tissues.

Monomer
One of the component units of a polymeric molecule.

Monoploid
Characterized by a single set of chromosomes.

Monosaccharide
The component unit of an oligosaccharide or polysaccharide.

Monosome
A chromosome in a diploid set with no homolog.

Monospecific
An antibody that recognizes a single antigen or epitope.

Monovalent
Possessing a single charge or valency.

Morphogenesis
Developmental changes in the inner structure and outer form of an organism.

Motif
A nucleic acid or protein sequence that is associated with a function.

Motor protein
A protein that moves along filament or polymer substrates in an ATP-dependent manner.

mRNA binding site
A ribosomal region that binds mRNA.

Multidimensional NMR
Three- and four-dimensional NMR methods for the detailed characterization of protein structure.

Multigene family
A set of sequence-related genes within a genome that evolved from a single ancestral gene by gene duplication and subsequent mutations.

Multimer
A molecular aggregate held together by noncovalent bonds.

Multiple alignment
An alignment of multiple sequences that inserts gaps into the individual sequences in order to align conserved sequences in the same column.

Multiple anomalous dispersion (MAD), multiple wavelength anomalous dispersion
An x-ray crystallographic phasing method that utilizes heavy atom information to solve biomacromolecular structures.

Multiple codon recognition
The ability of a tRNA to recognize more than one mRNA codon.

Multiplex assay
A procedure for the parallel analysis of pooled samples.

Multiplex fluorescent in situ hybridization (M-FISH)
The identification of chromosomes using combinatorially labeled fluorescent chromosomal probes in a wide array of colors. Chromosomal painting probes specifically hybridize with chromosome sequences and identify known bands.

Multiplicity of infection
The ratio of virus particles to cells in a system.

Multipotent
A cell or tissue able to form several different kinds of cells or tissues.

Multivesicular body
A lysosomal structure containing inner vesicles.

Mutagen
An agent that increases the frequency of mutation.

Mutagenesis
The production of changes in DNA sequence that affect the expression of genes or the structure of gene products.

Mutation
A heritable change in DNA sequence at the level of the gene, the chromosome, or the genome.

Myeloma
A tumor caused by the proliferation of immunoglobulin-synthesizing cells. Myelomas produce large amounts of a single (monoclonal) antibody, or the individual heavy or light chains.

NTop 
Naked DNA
Purified DNA with no associated proteins.

Nanofluidics
The use of silicon-based nanostructures capable to analyze single molecules with features comparable in size to DNA and proteins.

Nanomole
One billionth mole; 10-9 mole.

Nanopore detection
A high-throughput technique for the detection of differences in single DNA strands based on the use of an ionic current to pull DNA through a pore created by a channel protein.

Nanotechnology
A miniaturization technology based on the development of nanometer-scale machines to operate in molecular environments.

Native structure
The 3-D structure of a protein in a living system.

Natural selection
Changes in the occurrence of alleles within a population over time due to differential reproductive success of individual genotypes.

Negative control
The down-regulation or shutdown of gene transcription in response to the binding of negative regulatory elements.

Neoantigen
A cellular antigen acquired after transformation by an oncogenic virus.

Neoplasm
A tissue growth or tumor that may be benign or malignant.

Nerve growth factor (NGF)
A protein that stimulates the growth of neurons and the formation of neural networks.

Nested PCR
A second round of PCR amplification that utilizes primers located internally to those used in the first round of amplification.

Neural network
A computational method for optimizing for a desired property based on previous learning cycles (training).

Neuroma
A tumor arising in nerve cells.

Neuron
A cell specialized for the transmission of nerve impulses.

Neurotransmitter
A chemical released from the pre-synaptic terminus of an axon that diffuses across the synapse and binds to receptors in the post-synaptic membrane. Neurotransmitters are released from synaptic vesicles near the presynaptic cell membrane in response to the action potential.

Neutrophil
Phagocytic white blood cell produced in the bone marrow that plays a role in immune defense.

New chemical entity (NCE)
A compound capable of being patented.

Nick
A space introduced into a DNA strand by the loss of one or more nucleotides.

Nick translation
A DNA probe labeling technique based on the introduction of nucleotide gaps into one strand of double-stranded DNA by a treatment with a nuclease, followed by the use of a DNA polymerase with exonuclease activity to extend the gaps and replace the nucleotides.

Noncoding sequence
A nucleic acid segment that has no gene product and may play a role in structural organization.

Nonessential amino acid
An amino acid that may be synthesized by a cell or organism from simple chemical precursors. Nonessential amino acids are not required as nutrients.

Nonpolar
Lacking in polarity; characterized by an even distribution of positive and negative charges.

Nonproductive binding
The non-reactive binding of a substrate to the active site of an enzyme.

Nonprotein amino acid
An amino acid that is not a component of proteins.

Nonredundant database
A database in which redundant entries have been noted and merged.

Nonsense codon
One of three codons (UAA, UAG, UGA) that signal the termination of translation and release of the protein chain from the ribosome.

Nonsense mutation
A mutation that causes the formation of a nonsense codon and the truncation of the protein product.

Normalization
A database refinement process that organizes a database so that results obtained from queries to the database are always unambiguous.

Northern blot
Technique in which RNA fragments separated by electrophoresis are transferred to a membrane and probed with a labeled nucleic acid probe to detect a specific RNA.

Nuclear localization signal (NLS)
A short amino acid sequence that functions as a nuclear localization signal.

Nuclear magnetic resonance (NMR)
A spectroscopic technique used to determine the 3-D structure of small- to medium-sized proteins. NMR is based on resonant absorption of electromagnetic radiation by the magnetic dipole moments of atomic nuclei in an applied magnetic field.

Nuclear Overhauser effect (NOE)
A multidimensional NMR method for measuring spatial relationships within molecules based on the interaction between dipole moments of two nuclei in spatial proximity.

Nuclear pore
An opening in the nuclear envelope that joins the inner and outer nuclear membranes.

Nuclease
An enzyme that hydrolyzes ester linkages in nucleic acids.

Nucleic acid
A polynucleotide polymer consisting of deoxyribunucleotide units (DNA) or ribonucleotide units (RNA) joined by phosphodiester bonds.

Nucleocytoplasmic
Relating the nucleus to the cytoplasm.

Nucleoid
A compact body within a bacterium containing the genome.

Nucleolus
A dense body found in the cell nucleus. The nucleolus functions to transcribe and process ribosomal RNA and to assemble ribosomal precursors.

Nucleoplasm
The protoplasm within the nuclear envelope.

Nucleoprotein
Any complex of a protein with a nucleic acid (DNA or RNA).

Nucleoside
A molecule consisting of a nitrogen-containing purine or pyrimidine base attached to a ribose or a deoxyribose sugar.

Nucleosome
A chromosomal packing unit composed of a length of DNA wrapped around a histone core.

Nucleotide
The fundamental unit of nucleic acids. A nucleotide consists of a nitrogen-containing base attached to a pentose monosaccharide with one, two, or three phosphate groups attached by ester linkages to the saccharide moiety.

Nucleus (plural, nuclei)
An organelle containing chromosomes that is the site of cellular DNA synthesis and RNA replication.

Nuclide
A single isotope.

Nude mice
A mutant mouse strain that lacks a thymus gland and T lymphocytes. Nude mice are hairless due to a mutation at a linked locus.

Null mutation
A mutation that does not produce a transcript or protein product.

Null phenotype
The phenotype corresponding to a null mutation.

Nutraceutical
A nutrient that confers beneficial effects.

 OTop 
Ochre codon
The UAA codon, one of three codons that code for termination of transcription of a mRNA and release of the newly synthesized polypeptide chain from the ribosome.

Ochre suppressor
A mutation that produces a tRNA that inserts an amino acid at the site of the ochre termination codon, and allows translation to continue.

Ockham's razor, Occam's razor
A maxim stating an explanation should be based on a minimal number of assumptions.

Octamer
An eight-base sequence element typical of eukaryotic promoters that binds transcription factors; the set of eight histones that forms the nucleosome core.

Okazaki fragments
Short DNA fragments produced as DNA replication intermediates that are subsequently joined to form a single continuous strand of DNA.

Oligoclonal
Derived from a small number of clones.

Oligomer
A molecule containing a small number of covalently linked units; a multisubunit protein.

Oligonucleotide
A molecule consisting of a small number of nucleotide units.

Oligopeptide
A molecule consisting of a small number of amino acid units.

Oligosaccharide
A molecule consisting of a small number of monosaccharide units.

Oncogene
Any gene associated with cancer. Oncogenes are derived by the mutation of proto-oncogenes, normal cellular genes involved in growth control.

One hybrid system
A method for detecting protein-DNA interactions.

Ontology
The creation of a systematically ordered data structure that enhances exchange of information between computers and scientists. Ontologies enable the definition and sharing of domain-specific vocabularies.

Opal codon
The UGA codon, one of three codons that code for the termination of transcription of a mRNA and release of the newly synthesized polypeptide chain from the ribosome.

Open reading frame (ORF)
The length of DNA sequence between the translation start signal and the termination codon that can be translated into a protein; the phase in which nucleotides can be read in sets of three that results in a protein.

Operator
A regulatory DNA sequence that controls the transcription of structural genes.

Operon
A prokaryotic DNA region that coordinates the regulatory and structural sequences for a gene or set of related genes.

Opsonin
A serum protein that renders microorganisms and other foreign material more susceptible to phagocytosis.

Opsonization
Coating a particle with opsonin proteins.

Optical biosensor
A sensor that uses light to detect the effect of a chemical on a biological system.

Optical fiber
A glass or plastic fiber surrounded by a material with a lower index of refraction. Optical fibers transmit light from one end to the other by internal reflection.

Optical tweezers
A laser-based technique that utilizes minute forces exerted by light waves to measure and to manipulate biomolecules.

Organelle
A discrete subcellular structure with specialized function.

Origin of replication
A region of DNA necessary for the initiation of replication.

Orphan drug
A drug that treats a rare disease.

Orphan receptor
Receptor for which an in vivo ligand is not yet known.

Ortholog
A gene with similar function to a gene in an evolutionarily related species. The identification of orthologs is useful for gene function prediction.

Osteoblast
A cell that secretes the bone matrix.

Osteoclast
A mononucleate macrophage that breaks down the bone matrix and plays a role in bone remodeling.

Overlapping gene
A gene whose sequence overlaps that of another gene in the same or a different reading frame.

Oxidative phosphorylation
The phosphorylation of ADP to ATP in a process driven by the generation of a proton gradient in the mitochondrial inner membrane that drives ATP synthase.

PTop 
Packaging
The encapsulation of DNA by viral coat proteins.

Palindrome
An arrangement of symbols that reads the same backward as forward.

Palindromic sequence
A double-stranded DNA sequence with a two-fold rotational axis of symmetry (dyad symmetry).

Panning
An iterative method for selecting cells or clones based on successive rounds of target selection.

Parallel analysis
Simultaneous analysis of thousands of samples.

Paralog
A gene related to a similar gene by duplication within a genome. Paralogs tend to evolve new, related functions.

Parameters
User-derived values used to set the boundaries of an algorithm.

Parsing
The use of algorithms to analyze data into components.

Passive immunity
Immunity acquired by transfer of antibodies or T-lymphocytes from another individual.

Patch-clamp
A technique that uses a microelectrode to record current flow across a membrane.

Pathogen
A microorganism or other agent that causes disease.

Pathway
A series of related biochemical reactions.

Pattern
A nucleic acid or protein motif that is computationally detectable within aligned sequences.

Penetrance
The degree to which a genotype is expressed as a phenotype; also used to characterize the likelihood that a gene will result in a disease.

Peptidase
A protease that hydrolyzes peptide bonds.

Peptide
Two or more amino acids joined by a peptide bond.

Peptide bond
An amide bond formed between two amino acids by the linkage of the amino group of one amino acid to the carboxyl group of a second amino acid.

Peptide map, peptide fingerprint
A pattern produced by hydrolysis of a protein and 2-D mapping of the resulting peptide fragments.

Peptide nucleic acid (PNA)
A DNA mimic that incorporates a peptide-like polyamide backbone.

Peptidoglycan
A polymer that contains equal amounts of peptide and polysaccharide.

Peptidyl site (P site)
One of two sites in the large ribosomal subunit involved in protein translation.

Peptidyl transferase
A ribosomal enzyme that catalyzes peptide bond formation during protein synthesis.

Periplasm
The space between the bacterial cell membrane and the cell wall. Recombinant proteins secreted into the periplasmic space are readily released.

Perturbagen
A molecule or peptide that disrupts intracellular processes, providing information about the operation of pathways and networks within the cell.

Peta-
A prefix indicating 1015; a quadrillion.

PetaFLOP
A theoretical measure of computer speed that corresponds to a thousand trillion (1015) floating point operations per second.

Peyer's patch
A region of lymphoid tissue in the submucosa of the intestine that is rich in B cells and germinal centers.

Phage (bacteriophage)
A virus that infects bacterial hosts and may be utilized to introduce genes. Phages are widely used as cloning and expression vectors.

Phage display (peptide phage display)
A technique that fuses peptides to capsid proteins on the phage surface. Libraries of phage-displayed peptides may be screened for binding to specific ligands; determination of the gene sequence of the selected phage identifies the peptide sequence.

Phagemid
A phage-plasmid vector able to replicate as single- or double-stranded DNA.

Phagocytosis
An endocytic process based on the extension of cellular pseudopods that engulf target cells and tissue debris, forming phagosomes. Subsequent fusion with lysosomes generates phagolysosomes and results in the digestion of the particles.

Phagolysosome
The organelle formed by the fusion of a phagosome with a lysosome.

Phagosome
A cellular inclusion formed by the engulfment of cells or tissue debris during phagocytosis.

Pharmaceutical proteins
Proteins manufactured for use as drugs.

Pharmacogenomics
The evaluation of individual genomic variation in relation to the delivery and effectiveness of drugs. Knowledge of individual genotype and hence phenotype makes it possible to customize drugs and drug delivery methods for specific subgroups.

Pharmacokinetics
The study of the absorption, distribution, metabolism, and elimination of drugs.

Pharmacophore
The 3-D coordinates of atoms corresponding to pharmacologically active components of a drug molecule.

Pharming
The production of large quantities of useful proteins by transgenic animals or plants.

Phenome
All biochemical, physiological, and morphological characteristics of an organism.

Phenomics
The study of all possible phenotypes; the subject of functional genomics.

Phenotype
Measurable functional and structural characteristics of an organism as determined by the interaction of the genotype with the environment.

Phenotypic fingerprint
The overall biochemical, physiological, and morphological profile of an organism.

Phospholipid
Two fatty acids linked via glycerol phosphate to one of several polar groups.

Photoaffinity label
A label with a photoactivatable group that forms a covalent link with an adjacent protein upon illumination.

Photobiology
The study of the effects of light on living systems.

Photodynamic therapy (PDT)
A treatment based on the uptake by target cells of photoactivatable molecules that destroy the cells upon exposure to a specific light source.

Photolithography
A process that utilizes selective masking to generate light patterns that direct chemical transformations within a photosensitive surface.

Photoreactivation
The light-activated repair of DNA damage by DNA photolyase.

Photosynthesis
A biochemical process in which light absorbed by chlorophyll is utilized to build carbohydrate molecules.

Photosynthetic reaction center
The bacterial photosynthetic complex that transduces light to ATP.

Phototroph, photo-autotroph
An organism that uses light as a primary source of energy, synthesizing all organic requirements directly from inorganic precursors.

Phycocyanin
Blue pigment found in cyanobacteria and red algae.

Phycoerythrin
Red pigment found in cyanobacteria and red algae.

Phylogenetic profiling
A method for predicting the function of a protein that is based on the correlation of protein inheritance across different species. Any two proteins having similar phylogenetic profiles are likely to be involved in a common pathway or multi-protein complex.

Phylum (plural, phyla)
A major group within a kingdom. Members of a phylum share a common structure and organization.

Physical map
The mapping of restriction fragments or overlapping clones onto a chromosome.

Physiomics
The study of the complete set of interactions that produce the physiology of an organism.

Phytochemical
A biologically active molecule derived from herbs, vegetables, fruits, flowers, etc.

Phytochrome
A plant chromoprotein involved in the regulation of light-dependent growth processes.

Phytohormone
A plant hormone.

Picomole
One trillionth mole; 10-12 mole.

Piezoelectric
A material capable of transducing mechanical output to electrical signals or, alternatively, electrical signals to mechanical output. Piezoelectric devices are used in microsystems.

Plant embryogenesis
A plant cell culture technique that produces plant embryos from small pieces of plant tissue. Plant embryogenesis is a form of somatic cell embryogenesis, in which an embryonic program is initiated in a cell from an adult tissue.

Plant storage proteins
Proteins stored in seeds that are utilized as a source of amino acids during germination.

Plantibody
Antibody produced by genetically engineered plants.

Plaque
A clear zone in a layer of cells produced by the action of an agent that lyses the cells, such as a virus.

Plaque lift
A technique that uses a membrane to “lift” expressed proteins from clones growing on a plate. Screening of the membrane identifies the proteins, and the active clones.

Plasma cell
An antibody-secreting B-lymphocyte.

Plasma membrane
The lipid bilayer membrane that forms the boundary of a cell.

Plasmacytoma
A plasma cell tumor.

Plasmid
A DNA element that is able to replicate independently. Elements of bacterial plasmids are utilized in vectors.

Plasmid curing
The treatment of cells with a substance that interferes with plasmid replication.

Plasticity
The ability to develop or adapt in response to the environment.

Plastid
A double membrane-bound cytoplasmic organelle containing DNA found in plants. Plastids include chloroplasts and chromoplasts.

Plastidome
The total plastid complement of a cell.

Plectonemic coiling
The intertwining of the two strands of a double helix such that separation of the strands requires uncoiling.

Pleiomorphic
Having the ability to change shape.

Pleiotropic
Having multiple effects on phenotype.

Pluripotent
Capable of differentiating into several final differentiated cell types.

Plus end
The end of an actin filament to which monomers are added more rapidly.

Plus strand
A virus-specified RNA, or any strand of DNA or RNA with equivalent sequence. The complementary sequence is the minus strand.

Point mutation
A single base change.

Polar
The uneven distribution of postive and negative charges in small molecules, resulting in an electric dipole moment.

Polar zipper
A protein structural motif consisting of interactions between polar residues on separate subunits or separate proteins.

Poly(A), poly(A+)
An abbreviation for polyadenylate, or polymerized adenosines. Most mRNAs are terminated by poly(A) stretches. Binding of poly(A) regions by poly(T) is a widely used technique for the isolation of mRNA from cells.

Polyacrylamide gel
A matrix of acrylamide polymers cross-linked using bis-acrylamide. Polyacrylamide gels are used for the separation of nucleic acids and proteins by gel electrophoresis.

Polyacrylamide gel electrophoresis (PAGE)
Electrophoresis of nucleic acids and proteins through polyacrylamide gels.

Polyadenylation site
A processing signal at the 3' end of an RNA that specifies the addition of a stretch of adenines.

Polycation conjugate
A macromolecule with multiple positive charges conjugated to a protein that binds a cell receptor. Polycation conjugates are used to transport DNA into cells.

Polyclonal
Derived from multiple clones.

Polyclonal antibody
An antibody generated by the immune response to an antigen. Each epitope on the antigen is capable of causing the formation of a clone of B lymphocytes that will produce an antibody to that epitope.

Polyethylene glycol (PEG)
A water-soluble polymer used to solubilize proteins, and as a cell fusogen.

Polygenic, multigenic
Caused by the combined action of alleles of multiple genes.

Polymerase chain reaction (PCR)
A techique for the cyclic amplification of DNA segments by thermostable DNA polymerase. Following heat denaturation of the DNA, oligonucleotide primers complementary to flanking regions are annealed and extended, resulting in the synthesis of replicated DNA.

Polymorphism
The existence within a population of two alleles of a gene, where the frequency of the rare allele is greater than 1%, and not attributable to recurrent mutation.

Polymorphonuclear granulocytes
A collective name for neutrophils, basophils, and eosinophils.

Polymorphonuclear leukocytes (PMN)
Phagocytic white blood cells with a lobed nucleus.

Polypeptide
A chain of amino acids connected by peptide linkages. A polypeptide is longer than an oligopeptide, and may constitute an entire protein.

Polysome, polyribosome
Multiple ribosomes actively translating a single mRNA into polypeptides.

Population
Organisms of the same species that occupy the same area.

Population diffusion coefficient
The tendency of motile cells to diffuse through the environment.

Porin
A trimeric transmembrane protein that forms channels in the bacterial outer membrane. Similar porins are found in the mitochondrial outer membrane.

Position effect
A change in the expression of a gene due to translocation of the gene to a new position in the genome.

Positive control
The activation or up-regulation of transcription in response to the binding of a regulatory element.

Positive negative selection (PNS)
A laboratory technique that accelerates the identification of genetically engineered organisms that possess desired genetic changes by selecting against the organisms that do not have the desired characteristics.

Positive supercoiling
Superhelical turns of a DNA double helix molecule.

Post-transcriptional modification
Alteration of newly transcribed RNA within the nucleus, such as 5' capping, the splicing out of introns, and 3' polyadenylation.

Post-translational modification
Covalent modification of proteins following translation, including glycosylation, phosphorylation, sulfation, acetylation, and ribosylation.

Potocytosis
Small molecule transport across cell membranes by caveolae.

Pre-steady state kinetics, transient phase kinetics
The brief phase of an enzymatic reaction during which the concentration of the reactant-catalyst complex rises to the steady state value.

Prenylation
The additon of a prenyl moiety to a protein. The addition of prenyl groups regulates protein-membrane interactions.

Prey protein
One of two hybrid proteins used in two-hybrid protein-protein interaction assays.

Pribnow box
One of the two consensus sequences in the 5' promoter region of prokaryotic RNA that control the binding of RNA polymerase.

Primary antibody
An antibody generated against an antigenic target (a protein, peptide, carbohydrate, or other small molecule).

Primary culture
The culture of cells obtained directly from the tissue source.

Primary immune response
The response of the immune system to the first challenge by an antigen.

Primary RNA, pre-RNA
Newly transcribed RNA that has not been processed to mRNA. Primary RNAs undergo processing by spliceosomes to remove introns and ligate exons, resulting in a continuous mRNA sequence.

Primase
An RNA polymerase that forms oligoribonucleotide primers in the 5' to 3' direction. During DNA replication, primase primes the RNA-DNA sequences that become the Okazaki fragments.

Primer
Oligonucleotide that may be extended by DNA polymerase.

Primer extension
A method for finding the start site for gene transcription. Reverse transcriptase is used to extend a primer to the 5' region of a gene and the resulting fragments compared on a gel.

Primosome
A protein complex, consisting mainly of DNA helicase and primase, that unwinds the DNA helix prior to replication and synthesizes RNA primer sequences.

Prion
An abnormally folded protein that causes disease by inducing normal counterparts within the cell to fold in an abnormal manner and aggregate.

Proband
The first person to be studied, from whom genetic descent may be traced.

Procapsid
A virion precursor that consists only of the viral capsid without the nucleic acid.

Processive
The activity of an enzyme that progressively synthesizes or breaks down a polymeric molecule using successive cyclic reactions but does not dissociate from the template between cycles.

Processivity
The number of nucleotides polymerized before a polymerase dissociates from the template.

Prodrug
An inactive drug precursor that is activated by a biological process, such as enzymatic cleavage.

Product inhibition
The inhibition of an enzymatic reaction by the accumulation of the products of the reaction.

Productive binding
The binding of a substrate to the active site of an enzyme in a reactive manner.

Proenzyme
An inactive enzyme precursor that is activated by proteolysis; a zymogen.

Programmed cell death
A form of cell death essential for development that is based on a mechanism that requires protein synthesis.

Prohormone
An peptide hormone that is inactive until proteolytic cleavage.

Prokaryote
An organism lacking a nucleus and other membrane-bounded compartments.

Promoter
The DNA sequence bound by RNA polymerase and transcription factors during the initiation of transcription.

Proof-reading
An enzymatic mechanism that corrects errors in DNA synthesis.

Proprietary database
A copyrighted database accessible by subscription.

Prosthetic group
A non-protein structure that is bound tightly to a protein and is essential to the activity of the protein.

Protease
An enzyme that degrades proteins by hydrolyzing peptide bonds.

Proteasome
A large protein complex that degrades proteins that have been tagged for elimination, particularly those tagged by ubiquitination.

Protein
A linear biomacromolecule synthesized by ribosomes and consisting of a chain of amino acids in peptide linkage. Intracellular proteins have structural, regulatory, and catalytic functions; proteins secreted by cells have, in addition, intercellular signaling functions.

Protein affinity chromatography
A method for the direct characterization of protein-protein interactions.

Protein chips
Microarrays used to identify proteins and characterize protein function.

Protein domain
A structurally and functionally defined protein region. In proteins with multiple domains, the combination of the domains determines the function of the protein.

Protein expression
The translation and post-translational processing of proteins.

Protein family
A group of proteins related by evolution that share highly conserved sequence regions, 3-D structure, and function.

Protein fingerprint
The pattern of proteins in a cell or organism as determined by 2-D gel electrophoresis.

Protein linkage map
A protein-protein interaction network map.

Protein primary structure
The sequence of amino acid residues that form a protein.

Protein quaternary structure
The interaction of protein subunits to form functional multi-subunit proteins.

Protein secondary structure
The interactions between amino acids within a protein chain to form an a helix and b sheet structure.

Protein tertiary structure
The folding of a protein into a 3-D structure.

Protein-protein interactions
The network of interactions between proteins based on two-hybrid assays and other protein-binding data.

Proteoglycan
One or more glycosaminoglycans attached to a core protein.

Proteolysis
Cleavage of proteins by proteases.

Proteome
The dynamic protein complement of an organism, including all post-translational modifications and protein interactions.

Proteomics
Proteome-wide analysis of protein regulation, expression, structure, post-translational modification, interactions, and function. This study of proteins is important in biotechnology and drug discovery, because proteins are responsible for most tasks in the cell.

Proto-oncogene
Normal cellular gene, usually involved in growth control, from which an oncogene is derived as the result of a somatic mutation or viral recombination.

Protomer
A subunit of an oligomeric protein.

Protonophore
An ionophore that transports protons.

Protoplast
A plant, fungal, or bacterial cell from which the outer cell wall or membrane has been removed.

Prototroph
A microorganism strain that requires the same nutrients as the wild-type strain.

Provirus
A virus that is integrated into the host chromosome and does not cause lysis.

Pseudogene
A nonfunctional gene sequence that is related to a known gene but cannot be transcribed or translated due to mutations.

Pseudopod
A transient protrusion or retractile process associated with cell movement and feeding.

Pseudotyping
Process for changing the cell binding specificity of a virus by changing the capsid (envelope) proteins.

Pseudouridine
A minor nucleoside component of tRNA formed by post-transcriptional modification of uridine. Pseudouridine within the anticodon base pairs with adenine.

Psychrophile
An organism that grows optimally at low temperatures.

Pulsed field gel electrophoresis (PFGE)
A gel electrophoretic method for the separation of megabase fragments of DNA based on continuous alteration of the angle at which the electrical field is applied.

Purine
A double-ring basic compound that contains nitrogen. Adenine and guanine are purines found in DNA and RNA.

Puromycin
A nucleoside antibiotic that interrupts protein synthesis by incorporating into the polypeptide and causing premature release from the ribosome.

Pyrimidine
A single-ring basic compound that contains nitrogen. Cytosine and thymine are pyrimidines found in DNA; cytosine and uracil are pyrimidines in RNA.

QTop 
Quantal
Describes a biological system capable of only two responses.

Quantitative structure activity relationship (QSAR)
The relationship between the structure of a chemical and its pharmacologic action.

Quantitative trait locus (QTL)
The chromosomal location of one of a set of genes that collectively encode a quantitative trait that varies continuously across a population.

Quantum mechanics
A theory that explains the behavior of elementary particles, atoms, and energy in terms of probabilities.

Quantum yield, quantum efficiency
The probability of luminescence in a system.

Quencher
A substance that deactivates excited molecules by processes such as resonance energy transfer and complex formation.

Quenching
The reduction of luminescence of a sample by the addition of a quencher.

Query sequence
The nucleic acid or protein sequence used to search sequence databases in order to identify similar sequences from which function may be deduced.

RTop 
R loop
A structure formed when a complementary RNA pairs with one strand of double-stranded DNA at the start of transcription.

Racemic mixture, racemate
A mixture of equal amounts of the D- and L- enantiomers of a chiral compound.

Radioimmunoassay (RIA)
An assay that utilizes radiolabeled antigens or antibodies to quantitate antibody-antigen interactions.

Radiolabel
A radioactive ligand incorporated into a small molecule or biomolecule that enables detection and quantification of the molecule.

Rare cutter
A restriction enzyme that cuts at sites that occur infrequently within chromosomes.

Rational drug design (RDD)
The design of a drug molecule based on knowledge of the pharmacologically relevant characteristics of the target protein structure, as obtained by x-ray crystallographic methods.

Readthrough protein
The extended protein that results when an RNA termination codon is read through by a suppressor tRNA.

Receptor
A protein that binds an extracellular ligand. Binding of ligand to a cell-surface receptor alters the structure and activity, resulting in the initiation of a series of signal transduction events that modulate intracellular biochemical pathways.

Receptor mapping
The use of the known 3-D structure of a ligand to predict features of the complementary structure of the receptor. The model is continuously refined as data are acquired.

Recessive allele
An allele that is expressed in the phenotype of the organism only when present in the homozygous form.

Recombinant DNA
DNA molecules generated by cloning DNA fragments into vectors, transforming cells, and isolating clones that express the DNA fragment.

Recombinant protein
A protein generated using recombinant DNA technology.

Recombination
The formation of a new genotype by chromosome re-assortment or intrachomosomal crossing over.

Recursion
The repetition of a data-processing algorithm until a pre-set threshold is reached.

Refolding chromatography
A chromatographic technique for the rescue of misfolded proteins that have aggregated and become insoluble.

Regulatory gene
A gene encoding a DNA-binding protein that functions as an enhancer, a transcription factor, a repressor, or other modifier of gene expression.

Regulatory network
A network of interactions between molecules that is inferred from computational algorithms that identify relationships within data derived from large-scale gene expression and proteome analysis.

Regulatory region
A DNA sequence that controls the expression of a gene.

Regulome
The total interactions of the regulatory networks within a cell.

Relaxation
The self-adjustment of a molecular system to a new minimum free energy state after the perturbation of the system.

Relaxed DNA
Circular DNA that has an unwound loop. Relaxed DNA is less compact than supercoiled DNA and migrates more slowly during gel electrophoresis.

Relaxed form (R form)
A quaternary protein structure that has higher affinity for a ligand than the taut form.

Release factor (R factor)
A protein involved in the release of nascent polypeptide chains from the ribosome.

Renaturation
The return of a denatured molecule to the original native conformation.

Repetitive sequences
Repeated polynucleotide sequences. Repetive sequence is characteristic of satellite DNA, minisatellite DNA, transposons, and Alu sequences.

Replica plating
The production of identical bacterial colony patterns on a series of agar plates.

Replication
The synthesis of new deoxypolynucleotide strands.

Replisome
A large multi-protein complex that performs DNA replication.

Reporter gene
A gene used to reveal the function of potential regulatory sequences.

Repressor
A DNA-binding protein that prevents transcription of an adjacent gene.

Resolvase
An enzyme involved in the replicative transposition of elements in E. coli.

Restriction enzyme
An endonuclease that recognizes specific nucleotide sequences and cleaves DNA at these sites.

Restriction fragment length polymorphism (RFLP)
Variation in DNA sequence between individuals that is detectable by variation in the length of DNA fragments generated by digestion with restriction endonucleases.

Restriction map
A diagram of DNA indicating sites of cleavage by restriction enzymes.

Restriction site
The DNA sequence recognized and cleaved by a restriction endonuclease.

Retinoblastoma
A tumor of the retina.

Retrotransposon, retroposon
A transposable element that is incorporated into a chromosome by a mechanism that requires reverse transcriptase.

Reverse genetics
The use of phenotype or protein information to identify the gene encoding the protein.

Reverse gyrase
An enzyme with a DNA helicase and DNA topoisomerase domains that induces positive supercoiling into DNA.

Reverse micelle
The structure formed by amphipathic molecules in a nonpolar solvent. The hydrophilic regions of the molecules are sequestered in the interior of the micelle, and the hydrophobic regions are at the surface.

Reverse transcriptase
An enzyme that catalyzes the synthesis of deoxyribonucleotides into a sequence complementary to a pre-existent RNA template.

Reverse transcriptase-PCR (RT-PCR)
A technique based on the use of reverse transcriptase to copy cellular RNA sequences into DNAs that are subsequently amplified by the polymerase chain reaction.

Reverse two hybrid system
A method for studying protein-protein interactions in which interactions result in the increased transcription of a toxic marker causing growth inhibition. Reverse two hybrid methods can select for conditions that cause the dissociation of proteins.

Reversion
A second mutation that reverses a previous single point mutation.

rho (R) factor
A bacterial protein that facilitates transcription termination. rho factor is an ATP-dependent helicase that upon activation causes release of the mRNA from the DNA template.

rho (R) protein
A small GTPase that controls the polymerization of actin into filaments.

Ribonuclease (rNase)
Any nuclease that cleaves phosphodiester bonds in RNA. All ribonucleases are proteins, with the exception of Ribonuclease P, which is a ribonucleoprotein with ribozyme activity.

Ribonuclease P (rNase P)
A ribozyme that forms the 5'-phosphate terminus of tRNA by cleaving bases from the 5' end of the primary transcript. rNase P is a ribonucleoprotein complex.

Ribonucleic acid (RNA)
A long macromolecule formed from ribonucleotides. Functional classes include messenger RNA (mRNA), ribosomal RNA (rRNA), transfer RNA (tRNA), small nucleolar RNA (snoRNA), and other small RNAs.

Ribonucleoprotein (RNP)
A complex of a protein with RNA. Examples include snRNP, small nuclear ribonucleoprotein and hnRNP, heterogeneous nuclear ribonucleoprotein.

Ribophorin
A ribosome-binding protein found in the endoplasmic reticulum.

Riboproteomics
The systematic characterization of RNA-protein interactions that affect the splicing, transport, lifetime, and translation of RNAs.

Ribose
A pentose sugar that is a structural component of ribonucleic acid, riboflavin, and other nucleosides and nucleotides.

Ribosomal protein
Any protein component of a ribosomal subunit. S proteins are derived from the small ribosomal subunit, L proteins from the large ribosomal subunit.

Ribosomal RNA (rRNA)
An integral structural component of the large and small ribosomal subunits. The rRNA associated with the large subunit has been shown to be a ribozyme with peptidyl transferase activity.

Ribosome
A structure consisting of small and large ribonucleoprotein units that is the site of intracellular protein biosynthesis.

Ribosyl
A glycosyl group derived from ribose.

Ribosylation
The addition of a ribosyl residue.

Ribozyme
An RNA molecule that catalyzes RNA splicing.

Rifampicin
A derivative of rifamycin that inhibits bacterial transcription without affecting eukaryotic transcription.

RNA editing
The alteration of RNA transcripts to produce RNAs with sequences different from those encoded in the genome.

RNA polymerase
An enzyme that catalyzes the synthesis of ribonucleotides into a sequence complementary to a pre-existent DNA template.

RNA polymerase I
The RNA polymerase that transcribes ribosomal RNA (rRNA).

RNA polymerase II
The RNA polymerase that transcribes messenger RNA (mRNA).

RNA polymerase III
The RNA polymerase that transcribes transfer RNA (tRNA).

RNA splicing
The excision of introns from RNA during the formation of mRNA.

Rolling circle
A method for the replication of circular double-stranded DNA.

Rosetta Stone method
A comparative genomics method that utilizes information about fused multi-domain proteins in one species to predict potential interactions of homologous proteins in other species that correspond to the individual domains.

Rough endoplasmic reticulum (RER)
A region of the endoplasmic reticulum associated with ribosomes and involved in the synthesis of membrane proteins and secreted proteins.

 STop 
S phase
The stage of the cell division cycle during which DNA is synthesized.

S1 mapping (S1 nuclease mapping)
A technique for the removal of single-stranded regions of DNA and RNA from double-stranded hybrids of DNA and RNA.

S1 nuclease
An endonuclease that degrades single-stranded RNA or DNA to mononucleotides. S1 nuclease is useful for the removal of unpaired regions following hybridization.

Saccharomyces cerevisiae (S. cerevisiae), Baker's yeast
A budding yeast widely studied as a simple model for eukaryotic cells.

Sanger sequencing
A DNA sequencing method based on controlled interruption of replication by dideoxynucleotides.

Saponin
A glycosidic surfactant produced by plant cells.

Sarcoma
A malignant tumor of the connective tissue.

Satellite DNA
Highly repetitive, non-transcribed DNA regions in eukaryotic chromosomes that have a different sedimentatin coefficient than other nuclear DNA.

Scaffold
The molecular core common to all members of a combinatorial library; also proteins that are instrumental in the assembly of large 3-D structures.

Second messenger
A mediator that is generated within a cell in response to a signal transduction event at the cell surface.

Secondary antibody
An antibody that recognizes and binds a primary antibody. Secondary antibodies conjugated to enzymes and labels are key components of detection systems.

Secondary response
The immune response that follows the second exposure to a substance.

Secondary structure
The arrangement of a protein chain into regular hydrogen-bonded structures such as a helix or b sheet.

Secretory granule
A small single-membrane vesicle formed from the Golgi apparatus that transports newly synthesized proteins to the cell periphery, fuses with the cell membrane, and delivers the proteins to the extracellular space.

Selection
A cell culture method that enables cells with specific characteristics to be isolated from a mixture of cells.

Selection pressure
The intensity of natural genetic selection processes. Selection pressure may be measured by changes in gene frequency.

Self-organization
The dynamic organization and interaction of the molecular components of living systems; the development of complex structures by the iteration of simple behaviors by individual components using only local information.

Sense strand
The strand of DNA that acts as the template for RNA synthesis.

Sequenator
Device for determining the sequence of monomeric residues of a polymeric molecule.

Sequence analysis
The determination of the sequence of a nucleic acid, protein, or carbohydrate based on the fragmentation of the original molecule, the analysis of sequence, and the assembly and interpretation of the sequence information.

Sequence profile
A sequence pattern representation emerging from comparison of multiple aligned sequences.

Sequence tagged site (STS)
A short DNA sequence with a known chromosomal location that occurs once within the human genome.

Sequencer
Device for determining the sequence of monomeric residues of a polymeric molecule.

Sequestration enabling reagent
A reagent that sequesters starting materials or reaction by-products, in order to simplify removal from a reaction mixture.

Serial analysis of gene expression (SAGE)
A quantitative gene expression analysis method based on the concept that an mRNA transcript may be identified by a short subfragment or tag derived from the 3' region of the transcript.

Sex chromosome
The 23rd pair in a karyotype; females have two X chromosomes, males have an X and a Y chromosome.

Sex determination
The genetic specification of the sex of an individual by the genes of the X and Y chromosomes.

Shine-Dalgarno sequence
An mRNA sequence that precedes the translation initiation codon and is complementary to a ribosomal RNA .

Shotgun cloning
A genomic cloning method based on the generation of random DNA fragments that are cloned into vectors to form a genome library.

Shuttle vector
A DNA plasmid capable of replication in multiple host organisms.

Sigma (S) factor (sigma subunit)
A bacterial transcription initiation factor that promotes association of RNA polymerase to specific initiation sites.

Signal peptidase
An endopeptidase that removes the signal peptide following translocation of a protein.

Signal sequence
A short amino acid sequence that determines the localization of a protein within the cell.

Signal transduction
Relaying a signal by conversion from one form to another. The transduction of an extracellular signal to the cytoplasm by a cell surface receptor or a cytoplasmic receptor.

Signature
An alternative term for motif or pattern.

Silent mutation
A mutation in a codon that does not cause a change in the amino acid sequence of the translation product.

Simulated annealing
A molecular dynamics method that simulates the heating and cooling of a system in order to describe the most stable state.

Simulation
An emulation of biological systems with predictive value for research; a virtual biological system.

Single cell capture
The isolation of single cells from a tissue using laser microdissection.

Single chain antibody
A synthetic antibody based on a single chain.

Single domain antibody (Dab)
A synthetic antibody based on a single chain.

Single molecule detection
Observations of the dynamics of single molecules. Single molecule methods complement high-resolution information obtained by averaging molecular ensembles using NMR and from static molecules using x-ray crystallography.

Single nucleotide polymorphism (SNP)
Scattered single-base pair variations within the genetic code of the individuals of a population. SNPs determine ways that subpopulations within a species differ and provide information about variations of protein expression.

Single spanning
A protein with a single transmembrane sequence.

Single strand binding protein (SSB)
A protein that binds single-stranded DNA and stabilizes unwinding of the double helix.

Single stranded conformation polymorphism analysis (SSCP)
A method for identifying mutations using the rate of DNA migration in denaturing gels.

Small molecule array
A microarray for the screening of small molecules derived from combinatorial synthesis.

Smith-Waterman
A sensitive algorithm for identifying sequence similarities.

Smooth endoplasmic reticulum (SER)
A region of the endoplasmic reticulum involved in lipid synthesis.

SNARE hypothesis
A model for vesicular fusion.

snoRNP
Abbreviation for Small Nucleolar Ribonucleoprotein.

snRNP
Abbreviation for Small Ribonuclear Particle.

Snurposome
One of three distinct nucleolar regions that contain small nuclear ribonucleoproteins (snRNPs).

Solid phase extraction
A sample purification method based on the affinity of either the desired or undesired components of a reaction mixture for a solid material and subsequent filtration of the solid material from the reaction.

Solid support
An insoluble material to which reagents may be attached so that they may be readily separated from reaction by-products and solvents by filtration.

Solid-phase synthesis
A combinatorial chemical synthesis technique for the creation of libraries of diverse compounds that utilizes solid supports to separate compounds during synthesis, thus simplifying the identification of the resulting compounds.

Soluble support
A support for a reaction that is soluble under reaction conditions, but readily separable by some simple process. Examples of soluble supports include linear polymers such as polyethylene glycol and dendrimers.

Solution-phase synthesis
Liquid-phase combinatorial chemical synthesis techniques for the creation of libraries of diverse compounds.

Somatic cell
Any cell of an organism that is not a germ cell.

Somatic cell hybrid
A hybrid cell formed from the fusion of cells from different species. Somatic cell hybrids are utilized for gene mapping.

Somatic gene therapy
The delivery of genetically engineered genes to somatic cells in order to treat a disease.

Somatic mutation
A non-heritable genetic change occurring within a somatic cell, also known as an acquired mutation.

Sonic hedgehog
Proteins vital to pattern formation in several metazoan groups.

Southern blot
A technique that utilizes labeled DNA probes to identify DNA fragments that have been transferred to membrane filters following electrophoretic separation.

Southwestern blot
A blotting technique for the detection of DNA-protein interactions based on the use of labeled DNA to probe proteins transferred to membrane filters.

Speciation
The development of new species as a result of evolutionary processes.

Spectroscopy
The study of molecular or atomic structure of a substance by observation of its interaction with electromagnetic radiation.

Spindle fibers
Microtubules extending from each chromatid to opposite poles of the cell during mitosis. Spindle fibers separate the chromatids into daughter cells.

Splice junction
The RNA sequence at the exon-intron boundary.

Splice site
The base sequence at each end of an intron that determines the splice point. The site at the 5' end of the intron is the donor site and the site at the 3' end is the acceptor site.

Spliceosome
A ribonucleoprotein complex consisting of RNA and small nuclear ribonucleoproteins (snRNPs). The spliceosome accomplishes the splicing of primary RNA transcripts by excising introns and ligating the ends of exons, resulting in a mRNA transcription.

Splicing
The covalent linkage of DNA by DNA ligase; the process by which the spliceosome excises introns from RNA; the post-translation cleavage and ligation process that results in the excision of a protein intein and ligation of the ends created to form an extein.

Split gene
An interrupted gene.

Spotted array
Array generated by microspotting nucleic acids on a glass, plastic, or filter substrate.

Squamous cells
Flat cells that constitute the surface of the skin.

ssDNA
Single-stranded DNA.

Stable isotope
An isotope that does not undergo radioactive decay.

Start codon
The codon (AUG) that codes for the first amino acid residue of all proteins (formylmethionine).

Steady state kinetics
The analysis of an enzyme reaction during the interval when the concentration of intermediates is steady.

Steric hindrance
Hindrance of an enzymatic reaction by structural features of the substrate or the enzyme.

Stop codon
One of three codons (UGA, UAG, UAA) that code for termination of transcription of a mRNA and release of the newly synthesized polypeptide chain.

Strain
An organism that is geneticaly different from others of the same species. Also known as a cultivar.

Streptavidin
A tetrameric biotin-binding protein capable of binding four molecules of biotin per molecule. Streptavidin may be labeled with a fluorophore, an enzyme, or gold particle to facilitate detection.

Structural bioinformatics
The process of predicting the 3-D structure of a protein from comparison of primary sequence alignment, secondary structure prediction, homology modeling, threading prediction, NMR data, and crystallographic data.

Structural gene
A gene that encodes a protein.

Structural prediction
The prediction of the structure of a protein based on homology to a known protein structure.

Structural proteomics
The proteome-wide study of protein structure and function, based on the selection of a set of proteins representative of each major protein family, development of high-throughput approaches to crystallization screening, and x-ray diffraction analysis.

Structure based drug design (SBDD)
The design of a drug molecule based on knowledge of the pharmacologically relevant characteristics of the target protein structure, as obtained by x-ray crystallographic methods.

Subcellular fractionation
The isolation of intracellular organelles and and sub-organellar compartments.

Subclone
A DNA clone generated by transferring a cloned DNA fragment from one plasmid to another.

Submitochondrial particle (SMP)
An inside-out particle formed by the sonication of mitochondria. Inverted mitochondrial inner membrane vesicles are used to study processes that involve oxidative phosphorylation.

Submolecular
A chemical component that exists at a lower level of complexity than individual molecules (electrons, ions, free radicals).

Substituent
A molecular group that replaces another in a chemical reaction.

Substrate
A molecule acted upon by an enzyme.

Subtraction library
A library prepared by subtractive hybridization that allows the detection of differentially expressed RNAs.

Subtractive hybridization
A process that eliminates cDNAs shared by two libraries by hybridization. Unhybridized cDNAs represent RNAs that are differentially expressed in one library.

Subunit
A single unit of a multi-subunit protein.

Suicide gene
A gene that processes an inactive prodrug to a toxic form.

Superantigen
An antigen that activates a large percentage of T-lymphocytes.

Superfamily
A group of functionally or structurally related proteins.

Superhelix, supercoil
The form of the DNA helix in vivo, in which DNA duplex structures are twisted around each other to form a superhelical structure.

Suppressor gene
A gene that reverses the effect of a mutation in another gene.

Suppressor mutation
A secondary mutation that restores function lost due to mutation at another site.

Suppressor tRNA
A transfer RNA that recognizes a termination codon in an RNA and adds an amino acid residue instead of terminating the chain, generating a readthrough protein.

Supramolecular
Any chemical system that exists at a higher level of complexity than individual molecules (multi-enzyme complexes, organelles, membranes).

Surface plasmon resonance (SPR)
A biosensor system used for analyzing ligand binding and kinetics of specific molecules within complex mixtures without prior purification. Binding of a ligand to a biomolecule immobilized on a membrane results in changes in membrane surface plasmon resonance.

Surfactant, surface active agent
A substance that reduces the surface tension of a liquid. Detergents and emulsifiers are surfactants.

SWISS-PROT
A curated protein sequence base.

Symbiont hypothesis
The concept that mitochondria are the descendants of bacteria that once lived as symbionts within eukaryotic cells.

Symbiosis
A long-term association of different species that provides mutual benefit.

Synapse
The site of communication between neurons. The synapse may transmit an action potential by the release of a neurotransmitter that binds a ligand-gated channel on the post-synaptic cell, or may make a direct connection between cells via gap junctions.

Syncytium (plural, syncytia)
Multi-nucleate cells formed by the fusion of neighboring cells. Syncytia may form due to the expression of a viral fusion protein during viral replication.

Syndrome
A pattern of recognizable symptoms or signs characteristic of a disease.

Synergist
An agent that increases the effectiveness of a ligand or other agent.

Syngeneic
An antigenically identical organism.

Systematic evolution of ligands by exponential enrichment (SELEX)
A process that identifies aptamers by iterative enrichment for molecules capable of binding a target.

Systematic name
In enzyme nomenclature, a name that precisely defines the catalytic activity of an enzyme. The systematic name for an enzyme describes the substrate(s) and provides a description of the nature of the reaction (a word ending in “-ase”).

Systematics
Biological classification and nomenclature.

Systemic
Affecting the entire body rather than a single part.

Systems biology
Systems-level understanding of biological systems that takes into account complex interactions of gene, protein, and cell elements.

TTop 
T cell
A T-lymphocyte.

T cell receptor
A transmembrane protein on the surface of T cells that recognizes antigens associated with MHC proteins on the surface of phagocytes.

T suppressor cell
A cell that suppresses helper cells.

T-lymphocyte
A white blood cell derived from lymphoid stem cells in the thymus that is responsible for cell-mediated immunity and for stimulating B lymphocytes. T-lymphocyte subtypes include helper, suppressor, and cytotoxic T cells.

Tandem MS (MS/MS)
A mass spectroscopic method used for high-throughput analysis of protein sequence. Two mass spectrometers are linked in tandem so that the first fragments proteins into peptides, and the second fragments the peptides, enabling the determination of the amino acid sequence.

Tandem repeats
Multiple copies of the same base sequence on a chromosome.

Target
A DNA, RNA, or protein that is involved in a disease process and is a suitable target for therapeutic compound development.

Target validation
Verifying that a DNA, RNA, or protein is involved in a disease process and is a suitable target for therapeutic compound development.

TATA box
A consensus sequence in the 5' region of eukaryotic transcription promoter regions that controls the binding of RNA Polymerase II. The TATA box is also known as the Goldberg-Hogness box.

Taut form (T form)
A quaternary protein structure that has lower affinity for a ligand than the relaxed form.

Tautomer
One of a set of possible alternative structures.

Telomerase reverse transcriptase (TERT)
A ribonucleoprotein reverse transcriptase involved with telomere formation and elongation.

Telomere
A cap structure at the ends of chromosomes consisting of short repeated sequences with strand asymmetry in GC content, resulting in one G-rich strand and one C-rich strand.

Telophase
The final stage of mitosis or meosis during which nuclei form in the daughter cells.

Template
A molecule whose structure is a pattern for the synthesis of a complementary molecule.

Temporal gene
A gene that programs the development of a system, determining the activation of structural and regulatory genes in various cell types.

Tera-
A prefix indicating 10 to the power of 12; a trillion.

TeraFLOP
A measure of supercomputer speed equivalent to 10 to the power of 12 floating point operations per second.

Teratogen
An agent that causes congenital malformations in embryos.

Termination codon
One of three codons (UGA, UAG, UAA) that code for termination of transcription of an mRNA and release of the newly synthesized polypeptide chain.

Termination factor
Any protein involved in the termination of transcription or translation.

Thermophile
A microorganism that grows optimally in high-temperature environments.

Three-dimensional quantitative structure-activity relationship (3-D QSAR)
The statistical correlation of 3-D structure of a compound with its biological activity.

Three-hybrid system
A technique for the detection of complexes that involve three proteins; also used to refer to a technique for the detection of RNA-protein interactions.

Thymidine
A nucleoside form of thymine.

Thymine
A pyrimidine base present in DNA. Thymine base pairs with adenine.

Tiled array
A microarray consisting of thousands of overlapping oligonucleotides defining a continuous chromosomal region.

Tissue microarrays
Arrays consisting of tissue specimen cores.

Tissue profiling
A target validation process that compares gene expression in normal and disease tissues.

Tolerance
An attenuation of response to an agent or antigen.

Topoisomer
Macromolecular isomers that differ in topology.

Topology
The study of the deformability of intact structures.

Topomeric
Conformations that share the same backbone topology.

Total gene expression analysis (TOGA)
An automated gene expression analysis technique that is a hybrid of differential display and serial analysis of gene expression (SAGE).

Totipotent
A cell with the potential to become any other cell of an organism.

Toxicogenomics
The genome-wide study of the effects of toxic substances on gene and protein expression.

Toxicokinetics
The rate of uptake and transformation of potentially toxic substances within a living system.

Trans-acting factor
A protein transcription factor.

Trans-splicing
The splicing of RNA exons generated from both strands of DNA into a single transcript.

Transactivation
Activation of transcription by the binding of a transcription factor to a DNA regulatory sequence.

Transcript
An RNA synthesized from a DNA template.

Transcription
The synthesis by RNA polymerase of an RNA complement from a DNA template.

Transcription factor binding site
The DNA sequence that is recognized and bound by a transcription factor.

Transcriptional activator
A regulatory element that binds a DNA transcription control sequence to activate the transcription of genes.

Transcriptional repressor
A regulatory element that binds a DNA transcription control sequence to repress the transcription of genes.

Transcriptisome
A large multi-protein complex that carries out the transcription of RNA.

Transcriptome
All transcribed mRNAs within a cell.

Transcriptomics
The genome-wide study of mRNA expression levels.

Transduction
The transfer of bacterial genetic material between bacteria by a bacteriophage or phage vector.

Transfection
The introduction of DNA into a cell or organism using recombinant DNA technology.

Transfer RNA (tRNA)
An RNA class characterized by a three-nucleotide sequence (the anticodon) that is complementary to a three-nucleotide sequence in mRNA (the codon). Attachment of an amino acid forms the active aminoacyl tRNA which functions as a ribosomal adaptor during translation.

Transformant
A bacterial cell that has undergone transformation.

Transformation
The alteration of the heritable properties of a cell.

Transgene
A gene incorporated into the germline that functions as a normal gene.

Transgenic
A genetically altered organism that stably incorporates genes from another organism and can pass them on to succeeding generations.

Transglycosylation
The transfer of a glycosyl residue to a molecule with the formation of a new glycosidic linkage.

Transition
A mutation that consists of the replacement of one purine by another purine or one pyrimidine by another pyrimidine.

Transition state
The initial state of a substrate molecule bound to the active site of an enzyme. The transition state is followed by the formation of more stable intermediates prior to product formation.

Transition state analog
A molecule that mimics the transition state of an enzymatic reaction.

Translation
The process of protein synthesis, carried out by ribosomes, and directed by the sequence of mRNA as read out by tRNA adaptors.

Translocation
The transfer of a molecule across a membrane.

Transmembrane protein
A protein that traverses a membrane.

Transport protein
A protein that transports a molecule within a cell or within a biological fluid.

Transposable element
A DNA segment that moves from one region of a genome to another.

Transposase
An enzyme involved in the transfer of transposons within a genome.

Transposon
A transposable genetic element that moves as a unit and inserts at new locations.

Transversion
A mutation that consists of the replacement of a purine by a pyrimidine or vice versa.

Trehalose
A disaccharide found in microorganisms that is used to stabilize protein structure.

Triplex DNA
A triple-stranded form of DNA generated by binding an oligo that recognizes a DNA region to double-stranded DNA.

Tropism
The movement response of an organism to an external stimulus, such as heat or light.

Tumor
A growth consisting of differentiated cancer cells.

Tumor marker
A diagnostic marker for cancer.

Tumor necrosis factor
A cytokine produced by many cell types that causes cytolysis of tumor cells, and mediates the expression of genes involved in the defense against disease.

Turnover number
The number of product molecules produced per minute by an enzyme catalyzing a reaction at the maximum rate.

Two-dimensional electrophoresis
A technique used for the separation of complex protein mixtures. Proteins are separated in the first dimension on an isoelectric focusing gel, rotated 90 degrees, then separated by molecular weight using standard gel electrophoresis.

Two-hybrid system
A method for studying protein-protein interactions. The “bait” protein is fused to one domain of a transcription factor and the “prey” to the other domain. Interaction between bait and prey proteins brings the two domains of the transcription factor into proximity.

UTop 
Ubiquitin
A protein that is covalently attached to lysines of other proteins, tagging them for proteolysis within proteasomes. Multiple ubiquitin units may be ligated to the protein, forming a multiubiquitin chain.

Ubiquitination
The covalent modification of a protein by conjugation to ubiquitin, a process which targets the protein-ubiquitin complex for degradation by the proteasome.

Ultra-high-throughput system (UHTS)
A high-throughput system capable of processing 100,000 samples a day.

Unilamellar
Consisting of one layer, often used in reference to lipid monolayer structures.

Unwinding protein
A protein that binds single-stranded DNA, and stabilizes the unwinding of the helical structure.

Upstream
In the 5' direction from a given transcription start point.

Uracil
A nitrogenous base found in RNA. Uracil base pairs with adenine.

Uridine
A nucleoside form of uracil.

VTop 
Vaccine
Immunogenic material capable of stimulating active immunity or, in the case of DNA vaccines, of directing the synthesis of proteins that stimulate immunity. Vaccines may elicit both prophylactic (preventative) and therapeutic responses.

Vacuole
A cytosolic membrane-bounded structure containing liquids.

Van der Waals forces
Weak, long-range forces between nonpolar molecules.

Variable numbers of tandem repeats (VNTR)
A polymorphism resulting in variability in the number of sequence repeats between two individuals.

Vector
An automously replicating DNA element that is used to transfer genes into organisms and to shuttle genes between organisms.

Vesicle
A membrane-bound structure used to shuttle molecules within the membrane.

Virion
A complete viral particle comprising a nucleic acid core and a protein capsid.

Viroid
An autonomously replicating plant pathogen.

Virtual cell
A computational simulation of a living cell.

Virtual library
An combinatorial chemical library that is built in silico with the goal of evaluating possible structures.

Virtual screening
A combinatorial chemistry technique for the computational screening of compounds.

Virus
A nucleoprotein structure consisting of DNA or RNA surrounded by a protein capsid. Viruses are unable to synthesize proteins or generate energy and are dependent on host cells for the production of progeny.

Visualization
The graphic representation of data, patterns within data, or knowledge based on analysis of data patterns.

Voltage-gated ion channel
A transmembrane ion channel controlled by membrane potential.

WTop 
Western blot
A technique for the separation, immobilization, and detection of proteins, usually by a labeled antibody.

Wild-type
The naturally occurring phenotype of an organism.

Wobble
Non-specific base-pairing of the base at the 5' end of a tRNA anti-codon to alternative bases at the 3' end of a mRNA codon.

YTop
X chromosome
The sex chromosome that exists in paired form in females.

X chromosome inactivation
The inactivation of one of the two X chromosomes carried by females. The inactivation of the X chromosome occurs randomly throughout the embryo, resulting in cells that are mosaic with respect to which chromosome is active.

X-ray
An energy beam of very short wavelengths (0.1 to 1000 Å) produced by the bombardment of various materials with high velocity electrons.

X-ray crystallography
A technique for determining the 3-D structure of a molecule, based on the diffraction of x-rays by the crystallized form of the molecule. Computational analysis of the diffraction pattern produces an electron density map.

X-ray diffraction
The scattering of x-rays from a crystal, resulting in an interference pattern used to determine the structure of the crystal.

Xenobiotic
A synthetic chemical that affects living systems.

Xenograft
A graft between individuals of different species.

Xenopus laevis (X. laevis)
An African clawed toad used to study developmental biology.

Xenotropic virus
A virus that can be grown in a species different from the normal host species.

YTop
Yoctomole
One septillionth mole; 10-24 mole.

Yotta-
A prefix indicating 1024; a septillion.

ZTop 
Z-DNA
A left-handed helical form of DNA. Z-DNA has been found for sequences containing alternating C and G bases.

Zeptomole
One-sextillionth mole; 10-21 mole.

Zetta-
A prefix indicating 1021; a sextillion.

Zinc finger
A DNA-binding protein motif that contains residues that coordinate a zinc ion which creates a finger-like loop.

Zoo blot
A Northern blot of mRNA from multiple organisms.

Zoonosis
A disease that may be transmitted to humans from animals.

Zootype
A hypothetical pattern of gene expression shared across all animal phyla.

Zwitterion
A dipolar ion containing ionic groups of opposite charge.

Zymogen
An inactive enzyme precursor that is activated by proteolysis; a proenzyme.

X
You may login with either your assigned username or your e-mail address.
The password field is case sensitive.
Loading