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E

Electrophoresis
A method of separating large molecules (such as DNA fragments or proteins) from a mixture of similar molecules. An electric current is passed through a medium containing the mixture, and each kind of molecule travels through the medium at a different rate, depending on its electrical charge and size. Agarose and acrylamide gels are the media commonly used for electrophoresis of proteins and nucleic acids.

Electroporation
A process using high-voltage current to make cell membranes permeable to allow the introduction of new DNA; commonly used in recombinant DNA technology.
See also: transfection

Embryonic stem (ES) cells
An embryonic cell that can replicate indefinitely, transform into other types of cells, and serve as a continuous source of new cells.

Endonuclease
See: restriction enzyme

Enzyme
A protein that acts as a catalyst, speeding the rate at which a biochemical reaction proceeds but not altering the direction or nature of the reaction. Organisms could not function if they had no enzymes.

Epistasis
One gene interfers with or prevents the expression of another gene located at a different locus.

Escherichia coli
Common bacterium that has been studied intensively by geneticists because of its small genome size, normal lack of pathogenicity, and ease of growth in the laboratory.

Eugenics
The study of improving a species by artificial selection; usually refers to the selective breeding of humans.

Eukaryote
Cell or organism with membrane-bound, structurally discrete nucleus and other well-developed subcellular compartments. Eukaryotes include all organisms except viruses, bacteria, and bluegreen algae.
See also: prokaryote, chromosome.

Evolutionarily conserved
See: conserved sequence

Exogenous DNA
DNA originating outside an organism that has been introducted into the organism.

Exon
The protein-coding DNA sequence of a gene. The region of a gene that contains the code for producing the gene's protein. Each exon codes for a specific portion of the complete protein. In some species (including humans), a gene's exons are separated by long regions of DNA (called introns or sometimes "junk DNA") that have no apparent function.
See also: intron

Exonuclease
An enzyme that cleaves nucleotides sequentially from free ends of a linear nucleic acid substrate.

Expressed gene
See: gene expression

Expressed sequence tag (EST)
A short strand of DNA that is a part of a cDNA molecule and can act as identifier of a gene. Used in locating and mapping genes.
See also: cDNA, sequence tagged site


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