Essential Cell Biology 5th edition

G:8 Glossary
molecule is translated into the amino acid sequence of a
protein.
genetic instability
An increased rate of mutation often caused by defects
in the systems that govern the accurate replication and
maintenance of the genome; the resulting mutations
sometimes drive the evolution of cancer.
genetic map
A graphic representation of the order of genes in
chromosomes spaced according to the amount of
recombination that occurs between them.
genetic screen
Experimental technique used to search through a collection
of mutants for a particular phenotype.
genetics
The study of genes, heredity, and the variation that gives rise
to differences between one living organism and another.
genome
The total genetic information carried by all the
chromosomes of a cell or organism; in humans, the total
number of nucleotide pairs in the 22 autosomes plus the X
and Y chromosomes.
genomic library
Collection of cloned DNA molecules that represents the
entire genome of a cell.
genotype
The genetic makeup of a cell or organism, including which
alleles (gene variants) it carries.
germ line
The lineage of reproductive cells that contributes to the
formation of a new generation of organisms, as distinct
from somatic cells, which form the body and leave no
descendants in the next generation.
globular protein
Any protein in which the polypeptide chain folds into a
compact, rounded shape. Includes most enzymes.
gluconeogenesis
Set of enzyme-catalyzed reactions by which glucose is
synthesized from small organic molecules such as pyruvate,
lactate, or amino acids; in effect, the reverse of glycolysis.
glucose
Six-carbon sugar that plays a major
role in the metabolism of living cells.
Stored in polymeric form as glycogen
in animal cells and as starch in plant
cells. (See Panel 2–4, pp. 72–73.)
H
C
HO
CH 2 OH
C O OH
H
OH H
C
H
C C
H OH
glycocalyx
Protective layer of carbohydrates on the outside surface
of the plasma membrane formed by the sugar residues of
membrane glycoproteins, proteoglycans, and glycolipids.
glycogen
Branched polymer composed exclusively of glucose units
used to store energy in animal cells. Granules of this
material are especially abundant in liver and muscle cells.
glycolysis
Series of enzyme-catalyzed oxidation reactions in which
sugars are partially degraded and their energy is captured
by the activated carriers ATP and NADH. (Literally, “sugar
splitting.”)
glycosaminoglycan (GAG)
Polysaccharide chain that can form a gel that acts as a
“space filler” in the extracellular matrix of connective
tissues; helps animal tissues resist compression.
Golgi apparatus
Membrane-enclosed organelle in
eukaryotic cells that modifies the
proteins and lipids made in the
endoplasmic reticulum and sorts
them for transport to other sites.
gradient-driven pump
A protein that uses energy stored in the electrochemical
gradient of ions to actively transport a solute across a
membrane.
green fluorescent protein (GFP)
Fluorescent protein, isolated from a jellyfish, that is used
experimentally as a marker for monitoring the location and
movement of proteins in living cells.
growth factor
Extracellular signal molecule that stimulates a cell to
increase in size and mass. Examples include epidermal
growth factor (EGF) and platelet-derived growth factor
(PDGF).
GTP
Nucleoside triphosphate used in the synthesis of RNA and
DNA. Like the closely related ATP, serves as an activated
carrier in some energy-transfer reactions. Also has a special
role in microtubule assembly, protein synthesis, and cell
signaling.
GTP-binding protein
Intracellular signaling protein whose activity is determined
by its association with either GTP or GDP. Includes both
trimeric G proteins and monomeric GTPases, such as Ras.
H + pump
A protein or protein complex that uses energy supplied by
ATP hydrolysis, an ion gradient, or light to actively move
protons across a membrane.
haploid
Describes a cell or organism with only one set of
chromosomes, such as a sperm cell or a bacterium. (See
also diploid.)
haplotype block
A combination of alleles or other DNA markers that has been
inherited as a unit, undisturbed by genetic recombination,
across many generations.
helix
An elongated structure whose subunits twist in a regular
fashion around a central axis, like a spiral staircase.
hemidesmosome
Structure that anchors epithelial cells to the basal lamina
beneath them.
heterochromatin
Highly condensed region of an interphase chromosome;
generally gene-poor and transcriptionally inactive. (See also
euchromatin.)
heterozygous
Possessing dissimilar alleles for a given gene.
histone
One of a small group of abundant, highly conserved proteins
around which DNA wraps to form nucleosomes, structures
that represent the most fundamental level of chromatin
packing.
histone-modifying enzyme
Enzyme that catalyzes the covalent addition of a small
molecule, such as a methyl or acetate group, to a specific
amino acid side chain on a histone.
homolog
A gene, chromosome, or any structure that has a close
similarity to another as a result of common ancestry.