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cyclic AMP (cAMP):
Nucleotide that is generated from ATP in response to hormonal
stimulation of cell-surface receptors. cAMP acts as a signaling
molecule by activating A-kinase; it is hydrolyzed to AMP by
a phosphodiesterase.
cyclin:
Protein that periodically rises and falls in concentration in
step with the eucaryotic cell cycle. Cyclins activate crucial
protein kinases (called cyclin-dependent protein kinases) and
thereby help control progression from one stage of the cell
cycle to the next.
cyclin-dependent protein kinase (Cdk
protein):
Protein kinase that has to be complexed with a cyclin protein
in order to act; different Cdk-cyclin complexes are thought
to trigger different steps in the cell-division cycle by phosphorylating
specific target proteins.
cytochrome:
Colored, heme-containing protein that transfers electrons during
cellular respiration and photosynthesis.
cytokeratin:
Member of a family of intermediate filament proteins characteristic
of epithelial cells.
cytokine:
Extracellular signaling protein or peptide that acts as local
mediator in cell-cell communication.
cytokinesis:
Division of the cytoplasm of a plant or animal cell into two,
as distinct from the division of its nucleus (which is mitosis).
cytokinin:
One of a family of small molecules that regulate the growth
and development of plant cells.
cytoplasm:
Contents of a cell that are contained within its plasma membrane
but, in the case of eucaryotic cells, outside the nucleus.
cytoskeleton:
System of protein filaments in the cytoplasm of a eucarotic
cell that gives the cell shape and the capacity for directed
movement. Its most abundant components are actin filaments,
microtubules, and intermediate filaments.
cytosol:
Contents of the main compartment of the cytoplasm, excluding
membrane-bounded organelles such as endoplasmic reticulum and
mitochondria. Originally defined operationally as the cell fraction
remaining after membranes, cytoskeletal components, and other
organelles have been removed by low-speed centrifugation.
cytotoxic T cell:
Type of T lymphocyte responsible for killing infected cells.
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