B cell (B lymphocyte) Type of lymphocyte that makes antibodies.
bacteria (singular bacterium) Members of the Bacteria, one of the two major
divisions of procaryotes, the other being the Archea. Most exist as single cells
and some cause disease.
bacterial artificial chromosome (BAC) Cloning vector that can
accommodate large pieces of DNA up to 1 million base pairs.
bacteriophage (phage) Any virus that infects bacteria. Bacteriophages were
the first entities used for the study of molecular genetics and are now widely
used as cloning vectors.
bacteriorhodopsin Pigmented protein found in the plasma membrane of a saltloving
bacterium, Halobacterium halobium. It pumps protons out of the cell in
response to light.
basal Situated near the base. The basal surface of a cell is opposite the apical
surface.
basal body Short cylindrical array of microtubules plus their associated
proteins found at the base of a eucaryotic cell cilium or flagellum. Serves as a
nucleation site for the growth of the axoneme. Closely similar in structure to a
centriole.
basal lamina (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.
base A substance that can accept a proton in solution. The purines and
pyrimidines in DNA and RNA are organic nitrogenous bases and are often
referred to simply as bases.
base pair Two nucleotides in an RNA or DNA molecule that are held together
by hydrogen bonds for example, G pairs with C, and A with T or U.
basic Having the properties of a base.
benign Describes tumors that are self-limiting in their growth and noninvasive.
benzene Molecule composed of a six-membered ring of carbon atoms,
commonly drawn containing three alternating double bonds. The benzene ring
occurs as part of many biological molecules.
beta-catenin (b-catenin) Multifunctional cytoplasmic protein that is involved
in cadherin-mediated cell cell adhesion, linking cadherins to the actin
cytoskeleton. Can also act independently as a gene regulatory protein. Has an
important role in animal development as part of a Wnt signaling pathway.
beta sheet (b 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 b-pleated sheet.
binding site A region on the surface of one molecule (usually a protein or
nucleic acid) that can interact with another molecule through noncovalent
bonding.
biosphere The world of living organisms.
biotin Low-molecular-weight compound used as a coenzyme. Useful
technically as a covalent label for proteins, allowing them to be detected by the
egg protein avidin, which binds extremely tightly to biotin. (2 63.)
bivalent A duplicated chromosome paired with its homologous duplicated
chromosome at the beginning of meiosis.
black membrane Artificial planar lipid bilayer membrane.
blastomere One of the cells formed by the cleavage of a fertilized egg.
blastula Early stage of an animal embryo, usually consisting of a hollow ball
of cells, before gastrulation begins.
blotting Biochemical technique in which macromolecules separated on an
agarose or polyacrylamide gel are transferred to a nylon membrane or sheet of
paper, thereby immobilizing them for further analysis. (See Northern
blotting, Southern blotting, Western blotting.)
bond energy Strength of the chemical linkage between two atoms, measured
by the energy in kilocalories or kilojoules needed to break it.
bright-field microscope The normal light microscope in which the image is
obtained by simple transmission of light through the object being viewed.
brush border Dense covering of microvilli on the apical surface of epithelial
cells in the intestine and kidney. The microvilli aid absorption by increasing
the surface area of the cell.
budding yeast Common name often given to the baker's yeast Saccharomyces cerevisiae, a common experimental organism, which divides by budding off a
smaller cell.
