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

G:4 Glossary
Bcl2 family Family of intracellular proteins that either promote
or inhibit apoptosis by regulating the release of cytochrome
c and other mitochondrial proteins from the intermembrane
space into the cytosol.
BclX L 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.
benign Of tumors: self-limiting in growth, and noninvasive.
beta sheet (β sheet) Common structural motif in proteins in
which different sections of the polypeptide chain run alongside
each other, joined together by hydrogen-bonding between
atoms of the polypeptide backbone. Also known as a β pleated
sheet. (Figure 3–7)
beta-catenin (β-catenin) Multifunctional cytoplasmic protein
involved in cadherin-mediated cell–cell adhesion, linking
cadherins to the actin cytoskeleton. Can also act independently
as a transcription regulatory protein. Has an important role in
animal development as part of a Wnt signaling pathway.
BH3-only proteins The largest subclass of Bcl2 family
proteins. Produced or activated in response to an apoptotic
stimulus and promote apoptosis mainly by inhibiting antiapoptotic
Bcl2 family proteins.
bi-orientation The attachment of sister chromatids to
opposite poles of the mitotic spindle, so that they move to
opposite ends of the cell when they separate in anaphase.
binding site Region on the surface of one molecule (usually a
protein or nucleic acid) that can interact with another molecule
through noncovalent bonding.
BiP Endoplasmic reticulum (ER)-resident chaperone protein
member of the family of hsp70-type chaperone proteins.
Bithorax complex One of two gene clusters in Drosophila
that contain Hox genes; genes in the Bithorax complex control
the differences among the abdominal and thoracic segments of
the body.
bivalent A four-chromatid structure formed during meiosis,
consisting of a duplicated chromosome tightly paired with its
homologous duplicated chromosome.
blastomere One of the many cells formed by the cleavage of
a fertilized egg.
blastula Early stage of an animal embryo, usually consisting
of a hollow ball of epithelial cells surrounding a fluid-filled cavity,
before gastrulation begins.
blebbing Membrane protrusion formed when the plasma
membrane detaches locally from the underlying actin cortex,
allowing cytoplasmic flow and hydrostatic pressure within the
cell to push the membrane outward.
bone Dense and rigid connective tissue comprising a mixture
of tough fibers (type I collagen fibrils), which resist pulling forces,
and solid particles (calcium phosphate as hydroxylapatite
crystals), which resist compression.
brassinosteroids Class of steroid signal molecules in plants
that regulate the growth and differentiation of plants throughout
their life cycle via binding to a cell-surface receptor kinase to
initiate a signaling cascade.
bright-field microscope Normal light microscope in which
the image is obtained by simple transmission of light through
the object being viewed.
buffer Solution of weak acid or weak base that resists the pH
change that would otherwise occur when small quantities of
acid or base are added.
C3 The pivotal complement protein that is activated by the
early components of all three complement pathways (the
classical pathway, the lectin pathway, and the alternative
pathway). (Figure 24–7)
Ca 2+ pump (calcium pump, Ca 2+ ATPase) Transport protein
in the membrane of sarcoplasmic reticulum of muscle cells
(and elsewhere). Pumps Ca 2+ out of the cytoplasm into the
sarcoplasmic reticulum using the energy of ATP hydrolysis.
Ca 2+ -activated K + channel Opens in response to the raised
concentration of Ca 2+ in nerve cells that occurs in response
to an action potential. Increased K + permeability makes the
membrane harder to depolarize, increasing the delay between
action potentials and decreasing the response of the cell to
constant, prolonged stimulation (adaptation).
Ca 2+ /calmodulin-dependent kinase (CaM-kinase) Serine/
threonine protein kinase that is activated by Ca 2+ /calmodulin.
Indirectly mediates the effects of an increase in cytosolic Ca 2+
by phosphorylating specific target proteins. (Figure 15–33)
cadherin Member of the large cadherin superfamily of
transmembrane adhesion proteins. Mediates homophilic
Ca 2+ -dependent cell–cell adhesion in animal tissues. (Figure
19–3 and Table 19–1, p. 1037)
cadherin superfamily Family of classical and nonclassical
cadherin proteins with more than 180 members in humans.
calmodulin Ubiquitous intracellular Ca 2+ -binding protein that
undergoes a large conformation change when it binds Ca 2+ ,
allowing it to regulate the activity of many target proteins. In
its activated (Ca 2+ -bound) form, it is called Ca 2+ /calmodulin.
(Figure 15–33)
calnexin Carbohydrate-binding chaperone protein in
the endoplasmic reticulum (ER) membrane that binds to
oligosaccharides on incompletely folded proteins and retains
them in the ER.
calreticulin Carbohydrate-binding chaperone protein
in the endoplasmic reticulum (ER) lumen that binds to
oligosaccharides on incompletely folded proteins and retains
them in the ER.
CaM-kinase II Multifunctional Ca 2+ /calmodulin-dependent
protein kinase that phosphorylates itself and various target
proteins when activated. Found in most animal cells but is
especially abundant at synapses in the brain, and is involved in
some forms of synaptic plasticity in vertebrates. (Figure 15–34)
cancer stem cells Rare cancer cells capable of dividing
indefinitely.
cancer-critical genes Genes whose alteration contributes to
the causation or evolution of cancer by driving tumorigenesis.
capsid Protein coat of a virus, formed by the self-assembly of
one or more types of protein subunit into a geometrically regular
structure. (Figure 3–27)
carbohydrate layer The carbohydrate-rich zone on the
eukaryotic cell surface attributable to glycoproteins, glycolipids,
and proteoglycans of the plasma membrane.
carbon-fixation reaction Process by which inorganic carbon
(as atmospheric CO 2 ) is incorporated into organic molecules.
The second stage of photosynthesis. (Figure 14–40)
carcinogenesis The generation of cancer.