V gene segment Gene segment encoding most of the variable region of the
polypeptide chains of immunoglobulins and T cell receptors.
V (D) J joining Recombination process by which gene segments are brought
together to form a functional gene for a polypeptide chain of an
immunoglobulin or T cell receptor.
vacuole Very large fluid-filled vesicle found in most plant and fungal cells,
typically occupying more than a third of the cell volume.
van der Waals attraction Type of (individually weak) noncovalent bond that
is formed at close range between nonpolar atoms.
variable region Region of an immunoglobulin light or heavy chain that differs
from molecule to molecule; it comprises the antigen-binding site.
vector In cell biology, the DNA of an agent (virus or plasmid) used to transmit
genetic material to a cell or organism. (See also cloning vector, expression
vector.)
vegetal pole The end at which most of the yolk is located in an animal egg.
The end opposite the animal pole.
ventral Situated toward the belly surface of an animal, or towards the
underside of a wing or leaf.
vesicle Small, membrane-bounded, spherical organelle in the cytoplasm of a
eucaryotic cell.
vesicular transport Transport of proteins from one cellular compartment to
another by means of membrane-bounded intermediaries such as vesicles or
organelle fragments.
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. Many viruses cause disease.
voltage-gated cation channel Type of ion channel found in the membranes of
excitable cells (such as nerve cells and muscle) which opens in response to a
shift in membrane potential past a threshold value.