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:8 Glossary
nucleotide or amino acid most often found at each position.
Preservation of a sequence implies that it is functionally
important.
conservative site-specifc recombination A type of
DNA recombination that takes place between short, specific
sequences of DNA and occurs without the gain or loss of
nucleotides. It does not require extensive homology between
the recombining DNA molecules.
constant region In immunology: region of an immunoglobulin
or T cell receptor chain that has a constant amino acid
sequence.
constitutive secretory pathway Pathway present in all cells
by which molecules such as plasma membrane proteins are
continually delivered to the plasma membrane from the Golgi
apparatus in vesicles that fuse with the plasma membrane.
The default route to the plasma membrane if no other sorting
signals are present. (Figure 13–63)
contact-dependent signaling Form of intercellular signaling
in which signal molecules remain bound to the surface of the
signaling cell and influence only cells that contact it.
contractile ring Ring containing actin and myosin that forms
under the surface of animal cells undergoing cell division.
Contracts to pinch the two daughter cells apart. (Figure 17–42)
convergent extension Rearrangement of cells within a tissue
that causes it to extend in one dimension and shrink in another.
(Figure 21–50)
COPI-coated vesicles Coated vesicles that transport
material early in the secretory pathway, budding from Golgi
compartments.
COPII-coated vesicles Coated vesicles that transport
material early in the secretory pathway, budding from the
endoplasmic reticulum.
copy number variations (CNVs) A difference between two
individuals in the same population in the number of copies of
a particular block of DNA sequence. This variation arises from
occasional duplications and deletions of these sequences.
cortex The cytoskeletal network in the cortical region of the
cytosol just beneath the plasma membrane.
coupled reaction Linked pair of chemical reactions in which
the free energy released by one serves to drive the other.
(Figure 2–29)
covalent bond Stable chemical link between two atoms
produced by sharing one or more pairs of electrons.
(Panel 2–1, pp. 90–91)
CRE-binding (CREB) protein Transcription regulator that
recognizes the cyclic AMP response element (CRE) in the
regulatory region of genes activated by cAMP. On activation
by PKA, phosphorylated CREB recruits a transcriptional
coactivator (CREB-binding protein; CBP) to stimulate
transcription of target genes.
CRISPR A defense mechanism in bacteria using small
noncoding RNA molecules (crRNAs) to seek out and destroy
invading viral genomes through complementary base-pairing
and targeted nuclease digestion.
crista (plural cristae) A specialized invagination of the inner
mitochondrial membrane.
cross-linking glycan One of a heterogeneous group of
branched polysaccharides that help to cross-link cellulose
microfibrils into a complex network. Has a long linear backbone
of one sugar type (glucose, xylose, or mannose) with short side
chains of other sugars.
cross-presentation A process in which extracellular proteins
taken up by specialized dendritic cells can give rise to peptides
that can be presented by class I MHC proteins to cytotoxic
T cells.
crRNAs Small noncoding RNAs (≈30 nucleotides) that are the
effectors of CRISPR-mediated immunity in bacteria.
cryoelectron microscopy Technique for examining a thin
film of an aqueous suspension of biological material that
has been frozen rapidly enough to create vitreous ice. The
specimen is then kept frozen and transferred to the electron
microscope. Image contrast is low, but is generated solely by
the macromolecular structures present.
cryptochrome Plant flavoprotein sensitive to blue light.
Structurally related to blue-light-sensitive enzymes called
photolyases (involved in the repair of ultraviolet-induced DNA
damage) but do not have a role in DNA repair. Also found in
animals, where they have an important role in circadian clocks.
Cubitus interruptus (Ci) Latent transcription regulator that
mediates the effects of Hedgehog.
cyclic AMP (cAMP) Nucleotide that is generated from
ATP by adenylyl cyclase in response to various extracellular
signals. It acts as a small intracellular signaling molecule, mainly
by activating cAMP-dependent protein kinase (PKA). It is
hydrolyzed to AMP by a phosphodiesterase. (Figure 15–25)
cyclic AMP phosphodiesterase Specific enzyme that
rapidly and continuously destroys cyclic AMP, forming 5′-AMP.
(Figure 15–25).
cyclic AMP-dependent protein kinase (protein kinase A,
PKA) Enzyme that phosphorylates target proteins in response
to a rise in intracellular cyclic AMP. (Figure 15–26)
cyclic GMP (cGMP) Nucleotide that is generated from GTP
by guanylyl cyclase in response to various extracellular signals.
cyclic GMP phosphodiesterase Specific enzyme that
rapidly hydrolyzes and degrades cyclic GMP.
cyclin Protein that periodically rises and falls in concentration
in step with the eukaryotic cell cycle. Cyclins activate crucial
protein kinases (called cyclin-dependent protein kinases, or
Cdks) and thereby help control progression from one stage of
the cell cycle to the next.
cyclin-dependent kinase (Cdk) Protein kinase that has to
be complexed with a cyclin protein in order to act. Different
cyclin–Cdk complexes trigger different steps in the cell-division
cycle by phosphorylating specific target proteins. (Figure 17–10)
cyclin–Cdk complex Protein complex formed periodically
during the eukaryotic cell cycle as the level of a particular cyclin
increases. A cyclin-dependent kinase (Cdk) then becomes
partially activated. (Figures 17–10 and 17–11, and
Table 17–1, p. 969)
cyclosome see anaphase-promoting complex
cytochrome Colored heme-containing protein that transfers
electrons during respiration and photosynthesis.
cytochrome c Soluble component of the mitochondrial
electron-transport chain. Its release into the cytosol from the
mitochondrial intermembrane space also initiates apoptosis.
(Figure 14–26)
cytochrome c oxidase complex Third of the three electrondriven
proton pumps in the respiratory chain. It accepts