Essential Cell Biology 5th edition

G:6 Glossary
electrochemical gradient
Driving force that determines which way an ion will move
across a membrane; consists of the combined influence
of the ion’s concentration gradient and the membrane
potential.
electron
Negatively charged subatomic particle that occupies space
around an atomic nucleus (e – ).
electron microscope
Instrument that illuminates a specimen using beams of
electrons to reveal and magnify the structures of very small
objects, such as organelles and large molecules.
electron-transport chain
A series of membrane-embedded electron carrier molecules
that facilitate the movement of electrons from a higher to
a lower energy level, as in oxidative phosphorylation and
photosynthesis.
electronegativity
The tendency of an atom to attract electrons.
electrophoresis
Technique for separating a mixture of proteins or DNA
fragments by placing them on a polymer gel and subjecting
them to an electric field. The molecules migrate through
the gel at different speeds depending on their size and net
charge.
electrostatic attraction
Force that draws together oppositely charged atoms.
Examples include ionic bonds and the attractions between
molecules containing polar covalent bonds.
embryonic stem (ES) cell
An undifferentiated cell type derived from the inner cell
mass of an early mammalian embryo and capable of
differentiating to give rise to any of the specialized cell
types in the adult body.
endocytosis
Process by which cells take in materials through an
invagination of the plasma membrane, which surrounds
the ingested material in a membrane-enclosed vesicle. (See
also pinocytosis and phagocytosis.)
endomembrane system
Interconnected network of membrane-enclosed organelles
in a eukaryotic cell; includes the endoplasmic reticulum,
Golgi apparatus, lysosomes, peroxisomes, and endosomes.
endoplasmic reticulum (ER)
Labyrinthine membrane-enclosed
compartment in the cytoplasm of
eukaryotic cells where lipids and
proteins are made.
endosome
Membrane-enclosed compartment of a eukaryotic cell
through which material ingested by endocytosis passes on
its way to lysosomes.
entropy
Thermodynamic quantity that measures the degree of
disorder in a system.
enzyme
A protein that catalyzes a specific chemical reaction.
enzyme-coupled receptor
Transmembrane protein that, when stimulated by the
binding of a ligand, activates an intracellular enzyme (either
a separate enzyme or part of the receptor itself).
epigenetic inheritance
The transmission of a heritable pattern of gene expression
from one cell to its progeny that does not involve altering
the nucleotide sequence of the DNA.
epithelium (plural epithelia)
Sheet of cells covering an external surface or lining an
internal body cavity.
equilibrium
State in which the forward and reverse rates of a chemical
reaction are equal so that no net chemical change occurs.
equilibrium constant, K
For a reversible chemical reaction, the ratio of substrate to
product when the rates of the forward and reverse reactions
are equal.
euchromatin
One of the two main states in which chromatin exists
within an interphase cell. Prevalent in gene-rich areas, its
less compact structure allows access for proteins involved
in transcription. (See also heterochromatin.)
eukaryote
An organism whose cells have a distinct nucleus and
cytoplasm.
evolution
Process of gradual modification and adaptation that occurs
in living organisms over generations.
exocytosis
Process by which most molecules are secreted from
a eukaryotic cell. These molecules are packaged in
membrane-enclosed vesicles that fuse with the plasma
membrane, releasing their contents to the outside.
exon
Segment of a eukaryotic gene that is transcribed into RNA
and dictates the amino acid sequence of part of a protein.
exon shuffling
Mechanism for the evolution of new genes; in the process,
coding sequences from different genes are brought together
to generate a protein with a new combination of domains.
extracellular matrix
Complex network of polysaccharides (such as
glycosaminoglycans or cellulose) and proteins (such as
collagen) secreted by cells. A structural component of tissues
that also influences their development and physiology.
extracellular signal molecule
Any molecule present outside the cell that can elicit a
response inside the cell when the molecule binds to a
receptor.
FAD
A molecule that accepts electrons and hydrogen atoms
from an electron donor; see FADH 2 .
FADH 2
A high-energy electron carrier produced by reduction of
FAD during the breakdown of molecules derived from food,
including fatty acids and acetyl CoA.
fat
Type of lipid used by living cells to store metabolic energy.
Mainly composed of triacylglycerols. (See Panel 2–5, pp.
74–75.)
fat droplet
Large cluster of hydrophobic fats or oils that forms inside
the cells.
fatty acid
Molecule that consists of a
carboxylic acid attached to
a long hydrocarbon chain.
Used as a major source of energy during metabolism and as
a starting point for the synthesis of phospholipids.
feedback inhibition
A form of metabolic control in which the end product of