coenzyme Small molecule tightly associated with an enzyme that participates in the reaction that the enzyme catalyzes, often by forming a covalent bond to the substrate. Examples include biotin, NAD+, and coenzyme A.
cohesin, cohesin complex   Complex of proteins that holds sister chromatids together along their length before their separation. (Figure 17–19) coiled-coil   Especially stable rodlike protein structure formed by two or more α helices coiled around each other. (Figure 3–9) collagen   Fibrous protein rich in glycine and proline that is a major component of the extracellular matrix in animals, conferring tensile strength. 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.  (Figures 3–23 and 19–40) collagen fibril   A higher-order collagen polymer of fibrillar collagens that assemble into thin structures (10–300 nm in diameter) many hundreds of micrometers long in mature tissues.
colony-stimulating factor (CSF) General name for numerous signal molecules that control differentiation of blood cells.
colorectal cancer   Cancer arising from the epithelium lining the colon (the large intestine) and rectum (the terminal segment of the gut).
column chromatography   Technique for separation of a mixture of substances in solution by passage through a column containing a porous solid matrix. Substances are retarded to different extents by their interaction with the matrix and can be collected separately from the column. Depending on the matrix, separation can be according to charge, hydrophobicity, size, or the ability to bind to other molecules.
commensalism   Ecological relationship between microbes and their host in which the microbe benefits but offers no benefit and causes no harm.
committed precursor   Cell derived from a stem cell that divides for a limited number of times before terminally differentiating; also known as a transit amplifying cell.
complement system   System of blood proteins that can be activated by antibody–antigen complexes or pathogens to help eliminate the pathogens, by directly causing their lysis, by promoting their phagocytosis, or activating an inflammatory response. (Figure 24–7) complementary (1) Of nucleic acid sequences: capable of forming a perfect base-paired duplex with each other.  (FIgure 4–4) (2) Of other interacting molecules, such as an enzyme and its substrate: having biochemical or structural features that marry up, so that noncovalent bonding is facilitated. (Figure 2–3) complementation test   Test to determine whether two mutations that produce similar phenotypes are in the same or different genes. (Panel 8–2, pp. 487) complex oligosaccharides   Broad class of N-linked oligosaccharides, attached to mammalian glycoproteins in the endoplasmic reticulum and modified in the Golgi apparatus, containing N-acetylglucosamine, galactose, sialic acid, and fucose residues.
condensin, condensin complex   Complex of proteins involved in chromosome condensation prior to mitosis. Target for M-Cdk. (Figure 17–22) conditional mutation   Mutation that changes a protein or RNA molecule so that its function is altered only under some conditions, such as at an unusually high or unusually low temperature.
cone photoreceptor (cone) Photoreceptor cell in the vertebrate retina that is responsible for color vision in bright light.
confocal microscope   Type of light microscope that produces a clear image of a given plane within a solid object. It uses a laser beam as a pinpoint source of illumination and scans across the plane to produce a two-dimensional “optical section.” (Figure 9–19) conformation   The folded, three-dimensional structure of a polypeptide chain.