Molecular Biology of the Cell by Bruce Alberts, Alexander Johnson, Julian Lewis, David Morgan, Martin Raff, Keith Roberts, Peter Walter by by Bruce Alberts, Alexander Johnson, Julian Lewis, David Morg

Glossary G:3
on the basal lamina that separates the epithelium from other
tissue.
apoptosis Form of programmed cell death, in which a
“suicide” program is activated within an animal cell, leading to
rapid cell death mediated by intracellular proteolytic enzymes
called caspases.
apoptosome Heptamer of Apaf1 proteins that forms
on activation of the intrinsic apoptotic pathway; it recruits
and activates initiator caspases that subsequently activate
downstream executioner caspases to induce apoptosis.
aquaporin (water channel) Channel protein embedded
in the plasma membrane that greatly increases the cell’s
permeability to water, allowing transport of water, but not ions,
at a high rate across the membrane.
archaeon (plural arch[a]ea) (archaebacterium) Singlecelled
organism without a nucleus, superficially similar
to bacteria. At a molecular level, more closely related to
eukaryotes in genetic machinery than are bacteria. Archaea and
bacteria together make up the prokaryotes. (Figure 1–17)
ARF proteins Monomeric GTPase in the Ras superfamily
responsible for regulating both COPI coat assembly and clathrin
coat assembly. (Table 15–5, p. 854)
ARP (actin-related protein) complex (Arp 2/3 complex)
Complex of proteins that nucleates actin filament growth from
the minus end.
arrestin Member of a family of proteins that contributes to
GPCR desensitization by preventing the activated receptor from
interacting with G proteins and serving as an adaptor to couple
the receptor to clathrin-dependent endocytosis. (Figure 15–42)
astral microtubule In the mitotic spindle, any of the
microtubules radiating from the aster which are not attached to
a kinetochore of a chromosome.
asymmetric cell division Cell division in which some
important molecule or molecules are distributed unequally
between the two daughter cells, causing these cells to become
different from each other.
ATM (ataxia telangiectasia mutated protein) Protein
kinase activated by double-strand DNA breaks. If breaks are
not repaired, ATM initiates a signal cascade that culminates in
cell cycle arrest. Related to ATR.
ATP (adenosine 5′-triphosphate) Nucleoside triphosphate
composed of adenine, ribose, and three phosphate groups.
The principal carrier of chemical energy in cells. The terminal
phosphate groups are highly reactive in the sense that their
hydrolysis, or transfer to another molecule, takes place with the
release of a large amount of free energy. (Figure 2–33)
ATP synthase (F 1 F o ATPase) Transmembrane enzyme
complex in the inner membrane of mitochondria and the
thylakoid membrane of chloroplasts. Catalyzes the formation
of ATP from ADP and inorganic phosphate during oxidative
phosphorylation and photosynthesis, respectively. Also present
in the plasma membrane of bacteria.
ATR (ataxia telangiectasia and Rad3 related protein)
Protein kinase activated by DNA damage. If damage remains
unrepaired, ATR helps initiate a signal cascade that culminates
in cell cycle arrest. Related to ATM.
autoimmune disease Pathological state in which the body
mounts a disabling adaptive immune response against one or
more of its own molecules.
autophagosome Organelle surrounded by a double
membrane contains engulfed cytoplasmic cargo in the initial
stages of autophagy.
autophagy Digestion of cytoplasm and worn-out organelles
by the cell’s own lysosomes.
auxin Plant hormone, commonly indole-3-acetic acid, with
numerous roles in plant growth and development.
axon Long nerve cell projection that can rapidly conduct
nerve impulses over long distances so as to deliver signals to
other cells.
axoneme Bundle of microtubules and associated proteins
that forms the core of a cilium or a flagellum in eukaryotic cells
and is responsible for their movements.
bacterial artificial chromosome (BAC) Cloning vector that
can accommodate large pieces of DNA, typically up to 1 million
base pairs.
bacteriorhodopsin Pigmented protein found in the plasma
membrane of a salt-loving archaeon, Halobacterium salinarium
(Halobacterium halobium). Pumps protons out of the cell in
response to light.
bacterium (plural bacteria) (eubacterium) Member of
the domain bacteria, one of the three main branches of the
tree of life (archaea, bacteria, and eukaryotes). Bacteria and
archaea both lack a distinct nuclear compartment, and together
comprise the prokaryotes. (Figure 1–17)
Bak A main effector Bcl2 family protein of the intrinsic
pathway of apoptosis in mammalian cells that is bound to
the mitochondrial outer membrane even in the absence of an
apoptotic signal; activation is usually by activated pro-apoptotic
BH3-only proteins.
basal Situated near the base. Opposite the apical surface.
basal lamina (plural basal laminae) Thin mat of extracellular
matrix that separates epithelial sheets, and many other types
of cells such as muscle or fat cells, from connective tissue.
Sometimes called basement membrane. (Figure 19–51)
base (1) A substance that can reduce the number of protons
in solution, either by accepting H + ions directly, or by releasing
OH – ions, which then combine with H + to form H 2 O.
(2) The purines and pyrimidines in DNA and RNA are organic
nitrogenous bases and are often referred to simply as bases.
(Panel 2–2, pp. 92–93)
base excision repair DNA repair pathway in which single
faulty bases are removed from the DNA helix and replaced.
Compare nucleotide excision repair. (Figure 5–41)
base pair Two nucleotides in an RNA or DNA molecule that
are held together by hydrogen bonds—for example, G paired
with C, and A paired with T or U.
basement membrane Thin mat of extracellular matrix that
separates epithelial sheets, and many other types of cells such
as muscle or fat cells, from connective tissue. Also called basal
lamina. (Figure 19–51)
Bax A main effector Bcl2 family protein of the intrinsic
pathway of apoptosis in mammalian cells; located mainly
in the cytosol and translocates to the mitochondria only
after activation, usually by activated pro-apoptotic BH3-only
proteins.
B cell receptor (BCR) The transmembrane immunoglobulin
protein on the surface of a B cell that serves as its receptor for
antigen.
Bcl2 Anti-apoptotic Bcl2 family protein of the outer
mitochondrial membrane that binds and inhibits pro-apoptotic
Bcl2 family proteins and prevents inappropriate activation of the
intrinsic pathway of apoptosis.