chiasma (plural chiasmata) X-shaped connection visible between paired homologous chromosomes during meiosis. Represents a site of chromosomal crossing-over, a form of genetic recombination.
chlorophyll   Light-absorbing green pigment that plays a central part in photosynthesis in bacteria, plants, and algae.
chloroplast   Organelle in green algae and plants that contains chlorophyll and carries out photosynthesis.
cholera toxin   Secreted toxic protein of Vibrio cholerae responsible for causing the watery diarrhea associated with cholera. Comprises an A subunit with enzymatic activity and a B subunit that binds to host-cell receptors to direct subunit A to the host-cell cytosol.
cholesterol An abundant lipid molecule with a characteristic four-ring steroid structure. An important component of the plasma membranes of animal cells. (Figure 10–4) chromatin Complex of DNA, histones, and non-histone proteins found in the nucleus of a eukaryotic cell. The material of which chromosomes are made.
chromatin immunoprecipitation   Technique by which chromosomal DNA bound by a particular protein can be isolated and identified by precipitating it by means of an antibody against the protein. (Figures 8–66 and 8–67) chromosome   Structure composed of a very long DNA molecule and associated proteins that carries part (or all) of the hereditary information of an organism. Especially evident in plant and animal cells undergoing mitosis or meiosis, during which each chromosome becomes condensed into a compact rodlike structure visible in the light microscope.
cilium (plural cilia) Hairlike extension of a eukaryotic cell containing a core bundle of microtubules. Many cells contain a single nonmotile cilium, while others contain large numbers that perform repeated beating movements. Compare flagellum.
circadian clock   Internal cyclical process that produces a particular change in a cell or organism with a period of around 24 hours, for example the sleep-wakefulness cycle in humans.
cis face Face on the same or near side.
cis Golgi network (CGN) Network of fused vesicular tubular clusters that is closely associated with the cis face of the Golgi apparatus and is the compartment at which proteins and lipids enter the Golgi.
cis-regulatory sequences DNA sequences to which transcription regulators bind to control the rate of gene transcription. In nearly all cases, these sequences must be on the same chromosome (that is, in cis) to the genes they control. (Figure 7–18) cisternal maturation model One hypothesis for how the Golgi apparatus achieves and maintains its polarized structure and how molecules move from one cisterna to another. This model views the cisternae as dynamic structures that mature from early to late by acquiring and then losing specific Golgiresident proteins as they move through the Golgi stack with cargo.
citric acid cycle [tricarboxylic acid (TCA) cycle, Krebs cycle] Central metabolic pathway found in aerobic organisms. Oxidizes acetyl groups derived from food molecules, generating the activated carriers NADH and FADH2, some GTP, and waste CO2. In eukaryotic cells, it occurs in the mitochondria. (Panel 2–9, pp. 106–107) clamp loader   Protein complex that utilizes ATP hydrolysis to load the sliding clamp on to a primer–template junction in the process of DNA replication.