Gamete
Specialized haploid cell (in animals either a sperm or an egg) produced
by meiosis of germ cells; in sexual reproduction, union of a sperm and
an egg (fertilization) initiates the development of a new individual.
Ganglioside Any glycolipid containing
one or more N-acetylneuraminic acid (sialic acid) residues in its structure.
Gangliosides are found in the plasma membrane of eukaryotic cells and
are especially abundant in neurons; they confer a net negative charge
on most animal cells.
Gap junction Protein channels linking
cytoplasm of adjacent cells that allows ions and small molecules to flow
between cytopla는 of the cells.
Gastrin Peptide hormone secreted
by antral region of stomach that stimulates gastric acid secretion.
Gel electrophoresis Electrophoresis
performed in a gel matrix so that molecules of similar electric charge
can be separated on the basis of size.
Gel retardation A technique that
identifies a DNA fragment that has a bound protein by virtue of its decreased
mobility during gel electrophoresis.
Geminivirus One of the two groups
of DNA viruses that infect plants, the members of which have potential
as cloning vectors for some species of higher plants.
Gene Physical and functional unit
of heredity, which carries information from one generation to the next.
In molecular terms, a gene is the entire DNA sequence necessary for the
synthesis of a functional polypeptide or RNA molecule. In addition to
coding regions most genes also contain noncoding intervening sequences
(introns) and transcription-control regions..
Gene addition A genetic engineering
strategy that involves the introduction of a new gene or group of genes
into an organism.
Gene cloning Insertion of a fragment
of DNA, carrying a gene, into a cloning vector, and subsequent propagation
of the recombinant DNA molecule in a host organism.
Gene mapping Determination of the
relative positions of different genes on a DNA molecule.
Generation number The number of population
doublings (estimated from dilution at subculture) that a culture has undergone
since explantation. Necessarily contains an approximation of the number
of generations in primary culture
Generation time The interval from one point
in the cell division cycle to the same point in the cycle, one division
later. Distinct from doubling time or population doubling time, which
is derived from the total cell count of a population and therefore averages
different generation times, including the effect of non-growing cells.
Gene subtraction A genetic engineering
strategy that involves the inactivation of one or more of an organism’s
genes.
Gene therapy A method that attempts
to cure an inherited disease by providing the patient with a functioning
copy of the defective gene.
Genetic drift Spontaneous variation
in the sequence of duplicated genes that developed during evolution; also
called sequence drift.
Genetic engineering The use of experimental
techniques to produce DNA molecules containing new genes or new combinations.
Genetic fingerprinting A hybridization
technique that detects the organization of highly polymorphic target sequences
and which can be used to produce a banding pattern that is unique for
each individual.
Genetic association A term used to describe
the condition where particular genotypes are associated with other phenomena,
such as particular diseases.
Genetic restriction The term used to describe
the observation that lymphocytes and antigen-presenting cells cooperate
most effectively when they share particular MHC haplotypes.
Genetics The branch of biology devoted
to the study of genes.
Genome The complete set of genetic
material contained within the cell.
Genomic library A collection of
clones sufficient in number to include all the genes of a particular organism.
Genotype The total genetic characteristics
of a cell. The genetic material inherited from parents; not all of it
is necessarily expressed in the individual.
Germ line The genetic material which is passed
down through the gametes before it is modified by somatic recombination
or maturation.
Germinal centres Areas of secondary lymphoid
tissue in which B-cell differentiation and antibody class-switching occurs.
Glial cell Nonneuronal cell in CNS
also called neuroglial cell that helps regulate extracellular environment
of CNS.
Glucagon A peptide hormone produced
in the α cells of the pancreas that triggers the conversion of glycogen
to glucose by the liver and with insulin controls blood glucose levels.
Glycocalyx Glycosylated peptides, proteins,
and lipids, and glycosaminoglycans attached to the surface of the cell.
Glycogen A very long, branched polymer
composed exclusively of glucose units, which is the primary storage carbohydrate
in animal cells. It is found primarily in the liver and muscle.
Glycogenolysis Breakdown of glycogen
to glucose, which occurs primarily in liver and muscle cells. The process
is stimulated by a rise in cAMP following epinephrine stimulation of cells
and, in muscle, by a rise in Ca2+ following neuronal stimulation.
Glycolipid A class of molecules,
frequently found in the plasma membrane, in which a short carbohydrate
chain is covalently linked to a lipid.
Glycolysis Anaerobic conversion
of sugars to lactate or pyruvate in the cytosol with the production of
ATP. Further degradation via the citric acid cycle occurs in the mitochondrion
and is coupled to oxidative phosphorylation.
Glycoprotein A class of molecules
in which one or more oligosaccharide chains are covalently linked to a
protein; frequently found in the plasma membrane or secreted from the
cell.
G protein Any of numerous heterotrimeric
guanine nucleotide-binding proteins that usually are linked to a seven-spanning
receptor on the cell surface. Binding of hormone to the receptor converts
the inactive form with GDP bound to the a subunit to the active Ga×GTP
form, which in turn stimulates or inhibits an effector protein that generates
a second messenger or functions as an ion channel.
Granulocytes Three granule-shape cells in
blood or lymphatics; neutrophils, eosinophils and basophils.
Granulosa cell Cell that surrounds egg and
antrum in ovarian follicle, secretes estrogen and inhibin and has many
other functions.
Growing fork Site in double-stranded DNA
at which the template strands are separated and addition of deoxyribonucleotides
to each newly formed chain occurs; also called replication fork. As DNA
synthesis proceeds, the growing fork continuously moves in the direction
of synthesis of the leading strand.
Growth curve A semilog plot of cell number
on a log scale against time on a linear scale in a proliferating cell
culture. Usually divided into lag phase, before growth is initiated, log
phase, the period of exponential growth, and plateau, a stable cell count
achieved when the culture stops growing at a high cell density.
Growth cycle Growth interval from subculture
to the top of the log phase, ready for a further subculture.
Growth factor An extracellular polypeptide
molecule that binds to a cell-surface receptor triggering a signal-transduction
pathway leading to cell proliferation or, in other cases, to specific
differentiation responses. The receptors for many growth factors (e.g.,
epidermal growth factor, platelet-derived growth factor, insulin) are
receptor tyrosine kinases.
Graft versus host (GVH) disease A condition
caused by allogeneic donor lymphocytes reacting against host tissue in
an immunologically compromised recipient.
GTP (Guanosine 5’-triphosphate) A nucleotide
that is a precursor in RNA synthesis and also plays a special role in
protein synthesis, signal-transduction pathways, and microtubule assembly.
GTPase superfamily Group of guanine nucleotide-binding
proteins that cycle between an inactive state with bound GDP and an active
state with bound GTP. These proteins (including G proteins, Ras proteins,
and certain polypeptide elongation factors) function as intracellular
switch proteins.