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clathrin:
Protein that assembles into a polyhedral cage on the cytoplasmic
side of a membrane so as to form a clathrin-coated pit, which
buds off to form a clathrin-coated vesicle.
cleavage:
(1) Physical splitting of a cell into two.
(2) Specialized type of cell division seen in many early embryos
whereby a large cell becomes subdivided into many smaller cells
without growth.
Clone:
Population of cells or organisms formed by repeated (asexual)
division from a common cell or organism. Also used as a verb:
"to clone a gene" means to produce many copies of
a gene by repeated cycles of replication.
cloning vector:
Genetic element, usually a bacteriophage or plasmid, that is
used to carry a fragment of DNA into a recipient cell for the
purpose of gene cloning.
coated pit:
Invagination of the plasma membrane associated with a bristlelike
layer of protein on its cytoplasmic surface. Pinches off to
form a coated vesicle in the process of endocytosis.
coated vesicle:
Small membrane-bounded organelle formed by the pinching off
of a coated region of membrane. Some coats are made of clathrin,
whereas others are made from other proteins.
codon:
Sequence of three nucleotides in a DNA or messenger RNA molecule
that represents the instruction for incorporation of a specific
amino acid into a growing polypeptide chain.
coenzyme:
Srnall molecule tightly associated with an enzyme that participates
in the reaction that the enzyme catalyzes, often by forming a
transient covalent bond to the substrate. Examples include biotin,
NAD+, and coenzyme A.
coenzyme A :
Small molecule used in the enzymatic transfer of acyl groups in
the cell. (See also acetyl CoA.)
cofactor:
Inorganic ion or coenzyme that is required for an enzyme's activity.
coiled-coil:
Especially stable rodlike protein structure formed by two a
helices coiled around each other.
collagen:
Fibrous protein rich in glycine and proline that is a major component
of the extracellular matrix and connective tissues. Exists in
many forms: type I, the most common, is found in skin, tendon,
and bone; type II is found in cartilage; type IV is present in
basal laminae.
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