Ectopic pregnancy  Implantation and development of a fetus at a site other than the uterus.

Ectoderm  The outer germ layer of the embryo giving rise to the epithelium of the skin.

Edema  Accumulation of excess fluid in interstitial space.

Efferent  Carrying away from. opp. Afferent.

Eicosanoids  Products of arachidonic acid metabolism including prostaglandins, leukotrienes and thromboxanes.

Electron transport  Flow of electrons from reduced electron donors (e.g., NADH) to O₂ via a series of electron carriers located in the inner mitochondrial membrane, or from H₂O to NADP in the thylakoid membrane of plant chloroplasts. In mitochondria and chloroplasts, electron movement is coupled to pumping of H ions across the membrane, setting up the proton-motive force that drives the formation of ATP.

Electrophoresis  Separation method of molecules such as proteins or nucleic acids on the basis of their charge-to-mass ratio using electric force.

Electroporation A method for increasing the rate of DNA uptake by protoplasts through prior exposure to a high voltage which results in the temporary formation of small pores in the cell membrane.

Elongation factor  One of a group of non-ribosomal proteins involved in translation of mRNA following initiation. Functions include regulation of binding of an aminoacyl-tRNA to a ribosome and release of tRNA after addition of an amino acid to the growing peptide chain.

Embryogenesis  Early development of an individual from a fertilized egg (zygote). Following cleavage of the zygote, the major axes are established during the blastula stage; in the subsequent gastrula stage, the early embryo invaginates and acquires three cell layers.

Embryonic induction  The interaction of cells from two different germ layers, promoting differentiation, often reciprocal.

End-filling  Conversion of a sticky end to a blunt end by enzymatic synthesis of the complement to the single-stranded extension.

Endocrine gland  Group of cells that secrete into the extracellular space hormones that then diffuse into bloodstream; also called a ductless gland.

Endocytosis  Uptake of extracellular materials by invagination of the plasma membrane to form a small membrane-bounded vesicle (endosome). Receptor-mediated endocvtosis involves the specific uptake of a receptor-bound ligand typically by invagination of clathrin-coated pits on the plasma membrane of animal cells..

Endoderm  The innermost germ layer of the embryo giving rise to the epithelial component of organs such as the gut, liver, and lungs.

Endogenous opioid  Certain neuropeptides ¾ endorphin, dynorphin, and enkephalin.

Endogenous pyrogen  Cytokines (including IL-1, probably IL-6 and tumor necrosis factor) that act physiologically in the brain to cause fever.

Endoplasmic reticulum (ER)   Network of interconnected membranous structures within the cytoplasm of eukaryotic cells. Two forms can be distinguished cytologically: rough ER, which is associated with ribosomes and functions in the synthesis and processing of secretory and membrane proteins, and smooth ER, which lacks ribosomes and is involved in synthesis of lipids.

Endonuclease  An enzyme that breaks phosphodiester bond within a nucleic acid molecule.

Endorphin  An endogenous opioid; functions as neurotransmitter at synapses activated by opiate drugs and as paracrine agent and hormone.

Endothelium  An epithelial-like cell layer lining spaces within mesodermally derived tissues, such as blood vessels or lymphatics, and derived from the mesoderm of the embryo.

Endotoxin  Lipopolysaccharide produced by Gram-negative bacteria, which activates B cells and macrophages

Enkephalin  Peptide neurotransmitter at some synapses activated by opiate drugs; an endogenous opioid.

Enzyme induction  An increase in synthesis of an enzyme produced by, for example, hormonal stimulation.

Episome  A plasmid capable of integration into the host cell’s chromosome.

Epithelial  Used of a culture to imply cells derived from epithelium but often used more loosely to describe any cells of a polygonal shape with clear, sharp boundaries between cells. Pavement-like More correctly this should be termed “epithelioid” or “epithelial-like”

Epitheium  A covering or lining of cells, as in the surface of the skin or lining of the gut, usually derived from the embryonic endoderm or ectoderm but exceptionally derived from mesoderm, as with kidney tubules and mesothelium lining body cavities.

Epitopes  The parts of an antigen which contact the antigen binding site of antibody or the T-cell receptor

Epstein-Barr virus  Causal agent of Burkitt’s lymphoma and infectious mononucleosis, which has the ability to transform human B cells into stable cell lines.

Erythrocyte  Small biconcave blood cell that contains hemoglobin, transports O₂ and CO₂ to and from the tissues of vertebrates and (in mammals) lacks a nucleus.

Ethanol precipitation Precipitation of nucleic acid molecules by ethanol plus salt, used primarily as a means of concentrating DNA or RNA.

Ethidium bromide  A fluorescent chemical that intercalates between base pairs in a double-stranded DNA molecule, used in the detection of DNA.

Eubacteria  Prokaryotic organisms including the so-called true bacteria such as Escherichia coli and Salmonella typhimurium. Phylogenetically distinct from archaebacteria.

Euchromatin  Less condensed portions of chromatin, including most transcribed regions.

Eukaryotes  Class of organisms, including all plants, animals, fungi, yeast, protozoa, and most algae, that are composed of one or more cells containing a membrane-enclosed nucleus and organelles. Opp. Prokaryotes.

Euploid  Exact multiples of the haploid chromosome set. The correct morphology characteristic of each chromosome pair in the species from which the cells were derived is not implicit in the definition but is usually assumed to be the case. Otherwise it should be stated as “euploid but with some chromosomal aberrations”

Exocytosis  Release of intracellular molecules (e.g., hormones, matrix proteins) contained within a membrane-bounded vesicle by fusion of the vesicle with the plasma membrane of a cell. This is the process whereby most molecules are secreted from eukaryotic cells. Opp. Endocytosis.

Exon  Gene segment encoding protein.

Exonuclease An enzyme that sequentially removes nucleotides from the ends of a nucleic acid molecule.

Explant  A fragment of tissue transplanted from its original site and maintained in an artificial medium.

Expression cloning  Recombinant DNA techniques for isolating a cDNA or genomic segment based on functional properties of the encoded protein and without prior purification of the protein.

Expression vector  A cloning vector designed so that a foreign gene inserted into the vector will be expressed in the host organism.

Extracellular matrix  A usually insoluble network consisting of glycosaminoglycans, collagen, and various adhesive proteins (e.g., laminin, fibronectin), which are secreted by animal cells. It provides structural support in tissues and can affect the development and biochemical functions of cells.

Extrinsic  Coming from outside