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electrochemical gradient:
Driving force that causes an ion to move across a membrane due
to the combined influence of a difference in its concentration
on the two sides of the membrane and the electrical charge difference
across the membrane.
electron acceptor:
Atom or molecule that takes up electrons readily, thereby gaining
an electron and becoming reduced.
electron carrier:
Molecule such as cytochrome c that transfers an electron from
a donor molecule to an acceptor molecule.
electron donor:
Molecule that easily gives up an electron, becoming oxidized
in the process.
electron transport:
Movement of electrons from a higher to a lower enery level along
a series of electron carrier molecules, as in oxidative phosphorylation
and photosynthesis.
elongation factor:
Protein required for the addition of amino acids to growing
polypeptide chains on ribosomes.
embryogenesis:
Development of an embryo from a fertilized egg, or zygote.
endocrine cell:
Specialized animal cell that secretes a hormone into the blood;
usually part of a gland, such as the thyroid or pituitary gland.
endocytosis:
Uptake of material into a cell by an invagination of the plasma
membrane and its internalization in a membrane-bounded vesicle.
(See also pinocytosis and phagocytosis.)
endoplasmic reticulum (ER):
Labyrinthine, membrane-bounded compartment in the cytoplasm
of eucaryotic cells, where lipids are synthesized and membrane-bound
proteins are made.
endosome:
Membrane-bounded organelle in animal cells that carries materials
newly ingested by endocytosis and passes many of them on to
lysosomes for degradation.
endothelium:
Single sheet of highly flattened cells (endothelial cells) that
forms the lining of all blood vessels. Regulates exchanges between
the bloodstream and surrounding tissues and is usually surrounded
by a basal lamina.
enhancer:
Regulatory DNA sequence to which gene regulatory proteins bind,
influencing the rate of transcription of a structural gene that
can be many thousands of base pairs away.
entropy:
Thermodynamic quantity that measures the degree of disorder
in a system; the higher the entropy, the more the disorder.
enzyme:
Protein that catalyzes a specific chemical reaction.
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