Molecular Biology of the Cell by Bruce Alberts, Alexander Johnson, Julian Lewis, David Morgan, Martin Raff, Keith Roberts, Peter Walter by by Bruce Alberts, Alexander Johnson, Julian Lewis, David Morg

G:6 Glossary
chemical carcinogens Disparate chemicals that are
carcinogenic—due to the ability to cause mutations—when fed
to experimental animals or painted repeatedly on their skin.
chemical group Certain combinations of atoms—such as
methyl (–CH 3 ), hydroxyl (–OH), carboxyl (–COOH), carbonyl
(–C=O), phosphate (–PO 2– 3 ), sulfhydryl (–SH), and amino (–NH 2 )
groups—that have distinct chemical and physical properties
and influence the behavior of the molecule in which the group
occurs.
chemiosmotic coupling (chemiosmosis) Mechanism in
which an electrochemical proton gradient across a membrane
(composed of a pH gradient plus a membrane potential) is used
to drive an energy-requiring process, such as ATP production
or the rotation of bacterial flagella.
chemotaxis Movement of a cell toward or away from some
diffusible chemical.
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 FADH 2 , some GTP, and waste
CO 2 . 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.
class I MHC protein One of two classes of major
histocompatibility complex (MHC) protein. Found on the surface
of almost all vertebrate cell types, where it can present foreign
peptides derived from a pathogen such as a virus to cytotoxic
T cells. (Figures 24–35 and 24–36A)
class II MHC protein One of two classes of major
histocompatibility complex (MHC) protein. Found on the surface
of various antigen-presenting cells, where it presents peptides
to helper and regulatory T cells. (Figures 24–35 and 24–36B)
class switching Change from making one class of
immunoglobulin (for example, IgM) to making another class (for
example, IgG) that many B cells undergo during the course of
an adaptive immune response. Involves DNA rearrangements
called class-switch recombination. (Figure 24–30)
class-switch recombination An irreversible change at the
DNA level when a B cell switches from making IgM and IgD to
making one of the secondary classes of immunoglobulin.
classical cadherins Family of cadherin proteins, including
E-cadherin, N-cadherin, and P-cadherin, that are closely related
in sequence throughout their extracellular and intracellular
domains.
clathrin Protein that assembles into a polyhedral cage on the
cytosolic side of a membrane so as to form a clathrin-coated
pit, which buds off by endocytosis to form an intracellular
clathrin-coated vesicle. (Figure 13–6)
clathrin-coated pits Specialized regions typically occupying
about 2% of the total plasma membrane area at which the
endocytic pathway often begins.
clathrin-coated vesicles Coated vesicles that transport
material from the plasma membrane and between endosomal
and Golgi compartments.
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.
clonal selection From a population of T and B lymphocytes
with a vast repertoire of randomly generated antigen-specific
receptors, a given foreign antigen activates (selects) only those
lymphocyte clones that display a receptor that fits the antigen.
Explains how the adaptive immune system can respond to
millions of different antigens in a highly specific way.
(Figure 24–15)