Essential Cell Biology 5th edition

G:2 Glossary
antibody
Protein produced by B lymphocytes in response to a foreign
molecule or invading organism. Binds to the foreign
molecule or cell extremely tightly, thereby inactivating it or
marking it for destruction.
anticodon
Set of three consecutive nucleotides in a transfer RNA
molecule that recognizes, through base-pairing, the threenucleotide
codon on a messenger RNA molecule; this
interaction helps to deliver the correct amino acid to a
growing polypeptide chain.
antigen
Molecule or fragment of a molecule that is recognized by
an antibody.
antiport
Type of coupled transporter that transfers two different
ions or small molecules across a membrane in opposite
directions, either simultaneously or in sequence.
apical
Describes the top or the tip of a cell, structure, or organ; in
an epithelial cell, for example, this surface is opposite the
base, or basal surface.
apoptosis
A tightly controlled form of programmed cell death that
allows excess cells to be eliminated from an adult or
developing organism.
archaeon
Microscopic organism that is a member of one of the
two divisions of prokaryotes; often found in hostile
environments such as hot springs or concentrated brine.
(See also bacterium.)
asexual reproduction
Mode of reproduction in which offspring arise from a
single parent, producing an individual genetically identical
to that parent; includes budding, binary fission, and
parthenogenesis.
aster
Star-shaped array of microtubules emanating from a
centrosome or from a pole of a mitotic spindle.
atom
The smallest particle of an element that still retains its
distinctive chemical properties; consists of a positively
charged nucleus surrounded by a cloud of negatively
charged electrons.
atomic weight
The mass of an atom relative to the mass of a hydrogen
atom; equal to the number of protons plus the number of
neutrons that the atom contains.
ATP
Activated carrier that serves as the principal carrier of
energy in cells; a nucleoside triphosphate composed of
adenine, ribose, and three phosphate groups. (See Figure
2–26.)
ATP synthase
Abundant membrane-associated enzyme complex that
catalyzes the formation of ATP from ADP and inorganic
phosphate during oxidative phosphorylation and
photosynthesis.
autophagy
Mechanism by which a cell “eats itself,” digesting molecules
and organelles that are damaged or obsolete.
Avogadro’s number
The number of molecules in a mole, the quantity of
a substance equal to its molecular weight in grams;
approximately 6 × 10 23 .
axon
Long, thin extension that conducts electrical signals away
from a nerve cell body toward remote target cells.
bacteriorhodopsin
Pigmented protein found in abundance in the plasma
membrane of the salt-loving archaeon Halobacterium
halobium; pumps protons out of the cell, fueled by light
energy.
bacterium
Microscopic organism that is a member of one of the two
divisions of prokaryotes; some species cause disease.
The term is sometimes used to refer to any prokaryotic
microorganism, although the world of prokaryotes also
includes archaea, which are only distantly related to each
other. (See also archaeon.)
basal
Situated near the base; opposite of apical.
basal lamina
Thin mat of extracellular matrix, secreted by epithelial cells,
upon which these cells sit.
base
Molecule that accepts a proton when dissolved in water;
also used to refer to the nitrogen-containing purines or
pyrimidines in DNA and RNA.
base pair
Two complementary nucleotides in an RNA or a DNA
molecule that are held together by hydrogen bonds—
normally G with C, and A with T or U.
Bcl2 family
Related group of intracellular proteins that regulates
apoptosis; some family members promote cell death, others
inhibit it.
beta sheet (β sheet)
Folding pattern found in many
proteins in which neighboring
regions of the polypeptide chain
associate side-by-side with each
other through hydrogen bonds to
give a rigid, flattened structure.
bi-orientation
The symmetrical attachment of a sister-chromatid pair
on the mitotic spindle, such that one chromatid in the
duplicated chromosome is attached to one spindle pole and
the other is attached to the opposite pole.
binding site
Region on the surface of a protein, typically a cavity or
groove, that interacts with another molecule (a ligand)
through the formation of multiple noncovalent bonds.
biosynthesis
An enzyme-catalyzed process by which complex molecules
are formed from simpler substances by living cells; also
called anabolism.
bivalent
Structure formed when a duplicated chromosome pairs
with its homolog at the beginning of meiosis; contains four
sister chromatids.
buffer
Mixture of weak acids and bases that maintains the pH of a
solution by releasing and taking up protons.
C-terminus
The end of a polypeptide chain that carries a free carboxyl
group (–COOH).
Ca 2+ pump (or Ca 2+ ATPase)
An active transporter that uses energy supplied by ATP
hydrolysis to actively expel Ca 2+ from the cell cytosol.