G
(1) Guanine (or the corresponding nucleoside or nucleotide) in a
nucleic acid.
(2) Glycine (see amino acids).
G-actin
See actin.
(G+C)% value
See GC%.
G loop
If the DNA of BACTERIOPHAGE MU is extracted from virions obtained
by induction of a lysogenic population of bacteria and is then denatured and
re-annealed, a proportion of the resulting dsDNA molecules show a ‘bubble’ or
loop of unpaired strands in the G region of the DNA; this loop – the G loop
– reflects localized non-homology generated by inversion of the G segment
during lysogeny. (G loops are rarely observed in phage DNA derived from lytic
infections.)
G phases
(Of cell cycle) See cell cycle.
A
GTP-binding protein that relays signals from a plasma-membrane signal receptor,
known as a G-protein linked receptor, to other signal-transduction proteins
inside the cell. When such a receptor is activated, it in turn activates the G
protein, causing it to bind a molecule of GTP in place of GDP. Hydrolysis of
the bound GTP to GDP inactivates the G protein.
G-protein
linked receptor
A signal
receptor protein in the plasma membrane that responds to the binding of a
signal molecule by activating a G protein.
G1 phase
The first
growth phase of the cell cycle, consisting of the portion of interphase before
DNA synthesis begins.
G2 phase
The
second growth phase of the cell cycle, consisting of the portion of interphase
after DNA synthesis occurs.
gametangium pl. gametangia
(gam-eh-tanj-ee-um)
[Gk. gamein, to marry + L. tangere, to touch]
The reproductive organ of bryophytes, consisting of the male antheridium and female archegonium; a multichambered jacket of sterile cells in which gametes are formed.
The reproductive organ of bryophytes, consisting of the male antheridium and female archegonium; a multichambered jacket of sterile cells in which gametes are formed.
gamete
(gam-eet)
[Gk. wife]
A haploid egg or sperm cell; gametes unite during sexual reproduction to produce a diploid zygote.
A haploid egg or sperm cell; gametes unite during sexual reproduction to produce a diploid zygote.
gametophyte
(guh-mee-toh-fite)
The multicellular haploid form in organisms undergoing alternation of generations, which mitotically produces haploid gametes that unite and grow into the sporophyte generation.
The multicellular haploid form in organisms undergoing alternation of generations, which mitotically produces haploid gametes that unite and grow into the sporophyte generation.
ganglion pl. ganglia
(gang-lee-un)
(gang-lee-ah) [Gk. ganglion, a swelling]
A cluster (functional group) of nerve cell bodies in a centralized nervous system.
A cluster (functional group) of nerve cell bodies in a centralized nervous system.
gap
junction
A type of
intercellular junction in animal cells that allows the passage of material or
current between cells.
gap
phases
In the
cell cycle, the phases that precede (G1) and follow (G2)
the synthesis (S) phase in which DNA is replicated; in the G1 phase,
the cell doubles in size, and its enzymes, ribosomes, and other cytoplasmic
molecules and structures increase in number; in the G2 phase,
the replicated chromosomes begin to condense and the structures required for mitosis
or meiosis are assembled.
gastric
[Gk. gaster, stomach]
Pertaining to the stomach.
Pertaining to the stomach.
gastrin
A
digestive hormone, secreted by the stomach, that stimulates the secretion of
gastric juice.
gastrovascular
cavity
[Gk. gaster, stomach
+ L. vasculum, a small vessel]
The central digestive compartment, usually with a single opening that functions as both mouth and anus.
The central digestive compartment, usually with a single opening that functions as both mouth and anus.
gastrula
(gas-troo-la)
[Gk. gaster, stomach]
The two-layered, cup-shaped embryonic stage.
The two-layered, cup-shaped embryonic stage.
gastrulation
(gas-truh-lay-shun)
The formation of a gastrula from a blastula.
The formation of a gastrula from a blastula.
gated ion
channel
A
specific ion channel that opens and closes to allow the cell to alter its
membrane potential.
Gause's
principle
See Competitive exclusion principle.
gel
electrophoresis
(jell eh-lek-troh-for-ee-sis)
The separation of nucleic acids or proteins, on the basis of their size and electrical charge, by measuring their rate of movement through an electrical field in a gel.
The separation of nucleic acids or proteins, on the basis of their size and electrical charge, by measuring their rate of movement through an electrical field in a gel.
gene
[Gk. genos, birth,
race; L. genus, birth, race, origin]
A discrete unit of hereditary information consisting of a specific nucleotide sequence in DNA (or RNA, in some viruses).
A discrete unit of hereditary information consisting of a specific nucleotide sequence in DNA (or RNA, in some viruses).
gene
amplification
The
selective synthesis of DNA, which results in multiple copies of a single gene,
thereby enhancing expression.
gene
cloning
The
production of multiple copies of a gene.
gene flow
The loss
or gain of alleles from a population due to the emigration or immigration of
fertile individuals, or the transfer of gametes, between populations.
gene pool
The total
aggregate of genes in a population at any one time.
genetic
code
The
system of nucleotide triplets in DNA and RNA that carries genetic information;
referred to as a code because it determines the amino acid sequence in the
enzymes and other protein molecules synthesized by the organism.
genetic
drift
Changes
in the gene pool of a small population due to chance.
genetic
isolation
The
absence of genetic exchange between populations or species as a result of
geographic separation or of premating or postmating mechanisms (behavioral,
anatomical, or physiological) that prevent reproduction.
genetic
map
An
ordered list of genetic loci (genes or other genetic markers) along a
chromosome.
genetic
recombination
The
general term for the production of offspring that combine traits of the two
parents.
genome
(jee-nome)
The complete complement of an organism's genes; an organism's genetic material.
The complete complement of an organism's genes; an organism's genetic material.
genomic
imprinting
The
parental effect on gene expression. Identical alleles may have different
effects on offspring, depending on whether they arrive in the zygote via the
ovum or via the sperm.
genomic
library
A set of
thousands of DNA segments from a genome, each carried by a plasmid, phage, or
other cloning vector.
genotype
(jee-noh-type)
The genetic makeup of an organism.
The genetic makeup of an organism.
genus pl. genera
(jee-nus)
[L. genus, race, origin]
A taxonomic category above the species level, designated by the first word of a species' binomial Latin name.
A taxonomic category above the species level, designated by the first word of a species' binomial Latin name.
geographical
range
The
geographic area in which a population lives.
geological
time scale
A time
scale established by geologists that reflects a consistent sequence of
historical periods, grouped into four eras: Precambrian, Paleozoic, Mesozoic,
and Cenozoic.
germ
cells
[L. germinare, to
bud]
Gametes or the cells that give rise to gametes.
Gametes or the cells that give rise to gametes.
germination
[L. germinare, to
bud]
In plants, the resumption of growth or the development from seed or spore.
In plants, the resumption of growth or the development from seed or spore.
gibberellin
(jib-ur-el-in)
[Fr. gibberella, genus of fungi]
A class of related plant hormones that stimulate growth in the stem and leaves, trigger the germination of seeds and breaking of bud dormancy, and stimulate fruit development with auxin.
A class of related plant hormones that stimulate growth in the stem and leaves, trigger the germination of seeds and breaking of bud dormancy, and stimulate fruit development with auxin.
gill
A
localized extension of the body surface of many aquatic animals, specialized
for gas exchange.
gland
[L. glans,
glandis, acorn]
A structure composed of modified epithelial cells specialized to produce one or more secretions that are discharged to the outside of the gland.
A structure composed of modified epithelial cells specialized to produce one or more secretions that are discharged to the outside of the gland.
glial
cell
(glee-ul)
[Gk. glia, glue + L. cella, a chamber]
A nonconducting cell of the nervous system that provides support, insulation, and protection for the neurons.
A nonconducting cell of the nervous system that provides support, insulation, and protection for the neurons.
globular
protein
[L. dim.
of globus, a ball]
A polypeptide chain folded into a roughly spherical shape.
A polypeptide chain folded into a roughly spherical shape.
glomerulus
(gluh-mare-yoo-lus)
[L. glomus, ball]
A ball of capillaries surrounded by Bowman's capsule in the nephron and serving as the site of filtration in the vertebrate kidney.
A ball of capillaries surrounded by Bowman's capsule in the nephron and serving as the site of filtration in the vertebrate kidney.
glucagon
[Gk. glykys, sweet
+ ago, to lead toward]
A peptide hormone secreted by pancreatic endocrine cells that raises blood glucose levels; an antagonistic hormone to insulin.
A peptide hormone secreted by pancreatic endocrine cells that raises blood glucose levels; an antagonistic hormone to insulin.
glucocorticoid
A
corticosteroid hormone secreted by the adrenal cortex that influences glucose
metabolism and immune function.
glucose
[Gk. glykys, sweet]
A six-carbon sugar (C6H12O6); the most common monosaccharide in animals.
A six-carbon sugar (C6H12O6); the most common monosaccharide in animals.
glycerol
A
three-carbon molecule with three hydroxyl groups attached; a glycerol
molecule can combine with three fatty acid molecules to form a fat or an oil.
glycocalyx
(gly-koh-kay-liks)
A fuzzy coat on the outside of animal cells, made of sticky oligosaccharides.
A fuzzy coat on the outside of animal cells, made of sticky oligosaccharides.
glycogen
(gly-koh-jen)
[Gk. glykys, sweet + genos, race or descent]
An extensively branched glucose storage polysaccharide found in the liver and muscle of animals; the animal equivalent of starch.
An extensively branched glucose storage polysaccharide found in the liver and muscle of animals; the animal equivalent of starch.
glycolipids
[Gk. glykys, sweet
+ lipos, fat]
Organic molecules similar in structure to fats, but in which a short carbohydrate chain rather than a fatty acid is attached to the third carbon of the glycerol molecule; as a result, the molecule has a hydrophilic "head" and a hydrophobic "tail." Glycolipids are important constituents of the plasma membrane and of organelle membranes.
Organic molecules similar in structure to fats, but in which a short carbohydrate chain rather than a fatty acid is attached to the third carbon of the glycerol molecule; as a result, the molecule has a hydrophilic "head" and a hydrophobic "tail." Glycolipids are important constituents of the plasma membrane and of organelle membranes.
glycolysis
(gly-kol-eh-sis)
[Gk. glykys, sweet + lysis, loosening]
The splitting of glucose into pyruvate. Glycolysis is the one metabolic pathway that occurs in all living cells, serving as the starting point for fermentation or aerobic respiration.
The splitting of glucose into pyruvate. Glycolysis is the one metabolic pathway that occurs in all living cells, serving as the starting point for fermentation or aerobic respiration.
glycoprotein
[Gk. glykys, sweet
+ proteios, primary]
A protein with covalently attached carbohydrate.
A protein with covalently attached carbohydrate.
Golgi
apparatus
(goal-jee)
An organelle in eukaryotic cells consisting of stacks of flat membranous sacs that modify, store, and route products of the endoplasmic reticulum.
An organelle in eukaryotic cells consisting of stacks of flat membranous sacs that modify, store, and route products of the endoplasmic reticulum.
gonadotropins
(goh-nad-oh-troh-pinz)
[Gk. gone, seed + trope, a turning]
Hormones that stimulate the activities of the testes and ovaries; a collective term for follicle-stimulating and luteinizing hormones.
Hormones that stimulate the activities of the testes and ovaries; a collective term for follicle-stimulating and luteinizing hormones.
gonads
[Gk. gone, seed]
The male and female sex organs; the gamete-producing organs in most animals.
The male and female sex organs; the gamete-producing organs in most animals.
graded
potential
A local
voltage change in a neuron membrane induced by stimulation of a neuron, with
strength proportional to the strength of the stimulus and lasting about a
millisecond.
gradualism
A view of
Earth's history that attributes profound change to the cumulative product of
slow but continuous processes.
Gram
stain
A
staining method that distinguishes between two different kinds of bacterial
cell walls.
granum pl. grana
(gran-um)
[L. grain or seed]
A stacked portion of the thylakoid membrane in the chloroplast. Grana function in the light reactions of photosynthesis.
A stacked portion of the thylakoid membrane in the chloroplast. Grana function in the light reactions of photosynthesis.
gravitropism
(grav-eh-troh-piz-um)
[L. gravis, heavy + Gk. trope, turning]
A response of a plant or animal in relation to gravity.
A response of a plant or animal in relation to gravity.
greenhouse
effect
The
warming of planet Earth due to the atmospheric accumulation of carbon dioxide,
which absorbs infrared radiation and slows its escape from the irradiated
Earth.
gross
primary productivity (GPP)
The total
primary productivity of an ecosystem.
gross
productivity
A measure
of the rate at which energy is assimilated by the organisms in a trophic level,
a community, or an ecosystem.
ground
meristem
[Gk. merizein, to
divide]
A primary meristem that gives rise to ground tissue in plants.
A primary meristem that gives rise to ground tissue in plants.
ground
tissue system
A tissue
of mostly parenchyma cells that makes up the bulk of a young plant and fills
the space between the dermal and vascular tissue systems.
growth
factor
A protein
that must be present in the extracellular environment (culture medium or animal
body) for the growth and normal development of certain types of cells.
guard
cell
A
specialized epidermal plant cell that forms the boundaries of the stomata.
guttation
The
exudation of water droplets caused by root pressure in certain plants.
gymnosperm
(jim-noh-spurm)
[Gk. gymnos, naked + sperma, seed]
A vascular plant that bears naked seeds not enclosed in any specialized chambers.
A vascular plant that bears naked seeds not enclosed in any specialized chambers.
Tags:
G protein
gel electrophoresis
Genetic drift
genomic imprinting
glomerulus
gross primary productivity
Guttation