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Glossary

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.