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:34 Glossary
vesicle transport model One hypothesis for how the Golgi
apparatus achieves and maintains its polarized structure and
how molecules move from one cisterna to another. This model
holds that Golgi cisternae are long-lived structures that retain
their characteristic set of Golgi-resident proteins firmly in place,
and cargo proteins are transported from one cisterna to the
next by transport vesicles.
vesicular transport Transport of proteins from one cell
compartment to another by means of membrane-bounded
intermediaries such as vesicles or organelle fragments.
V gene segment A DNA sequence encoding most of
the variable region of an immunoglobulin or T cell receptor
polypeptide chain. There are many different V gene segments,
one of which becomes joined to a D or J gene segment by
somatic recombination when an individual lymphoid progenitor
cell begins to differentiate into a B or T lymphocyte.
(Figure 24–28)
virulence factor Protein, encoded by a virulence gene, that
contributes to an organism’s ability to cause disease.
virulence gene Gene that contributes to an organism’s ability
to cause disease.
virus Particle consisting of nucleic acid (RNA or DNA)
enclosed in a protein coat and capable of replicating within a
host cell and spreading from cell to cell. (Figure 23–11)
virus receptor Molecule on the host cell surface to which
virus surface proteins bind to enable binding of virus to the cell
surface.
voltage-gated cation channel Type of ion channel found
in the membranes of electrically excitable cells (such as nerve,
endocrine, egg, and muscle cells). Opens in response to a shift
in membrane potential past a threshold value.
voltage-gated K + channel Ion channel in the membrane of
nerve cells that opens in response to membrane depolarization,
enabling K + efflux and rapid restoration of the negative
membrane potential.
voltage-gated Na + channel Ion channel in the membrane
of nerve and skeletal muscle cells that opens in response to a
stimulus causing sufficient depolarization, allowing Na + to enter
the cell down its electrochemical gradient
v-SNAREs Transmembrane SNARE protein, comprising a
single polypeptide chain, usually found in vesicle membranes
where it interacts with t-SNAREs in target membranes.
V-type pumps Turbine-like protein machines constructed
from multiple different subunits that use the energy of ATP
hydrolysis to drive transport across a membrane. The V-type
proton pump transfers H + into organelles such as lysosomes to
acidify their interior. (Figure 11–12)
WASp protein Key target of activated Cdc42. Exists in
an inactive folded conformation and an activated open
conformation; association with Cdc42 stabilizes the open form,
enabling binding to the Arp 2/3 complex and enhancing actinnucleating
activity.
Wee1 Protein kinase that inhibits Cdk activity by
phosphorylating amino acids in the Cdk active site. Important in
regulating entry into M phase of the cell cycle.
Western blotting Technique by which proteins are separated
by electrophoresis and immobilized on a paper sheet and then
analyzed, usually by means of a labeled antibody. Also called
immunoblotting.
white blood cell General name for all the nucleated blood
cells lacking hemoglobin. Also called leukocytes. Includes
lymphocytes, granulocytes, and monocytes. (Figure 22–27)
Wnt protein Member of a family of secreted signal proteins
that have many different roles in controlling cell differentiation,
proliferation, and gene expression in animal embryos and adult
tissues.
Wnt/β-catenin pathway Signaling pathway activated by
binding of a Wnt protein to its cell-surface receptors. The
pathway has several branches. In the major (canonical) branch,
activation causes increased amounts of β-catenin to enter the
nucleus, where it regulates the transcription of genes controlling
cell differentiation and proliferation. Overactivation of the
Wnt/β-catenin pathway can lead to cancer. (Figure 15–60)
X-inactivation Inactivation of one copy of the X chromosome
in the somatic cells of female mammals.
X-inactivation center (XIC) Site in an X chromosome at
which inactivation is initiated and spreads outward.
x-ray crystallography Technique for determining the threedimensional
arrangement of atoms in a molecule based on the
diffraction pattern of x-rays passing through a crystal of the
molecule. (Figure 8–21)
zygote Diploid cell produced by fusion of a male and female
gamete. A fertilized egg.