Online Biology Dictionary - G

g (1) gram; (2) guanine; (3) gravitational constant.

G (1) guanine; (2) glycine.

G3P Glyceraldehyde-3-phosphate.

G6P Glucose-6-phosphate.

ΔG Gibbs free energy.

GABA γ-aminobutyric acid, the most important inhibitory neurotransmitter in the central nervous system of mammals.

galactagogue /guh-LACK-tuh-goag, -gawg/ (1) stimulating milk flow; (2) a stimulant of milk flow.

galactose (Gal) /guh-LACK-tohs, -oze/ A monosaccharide or simple hexose sugar; an isomer of glucose, and a component of disaccharide lactose, as well as various mucoproteins and cerebrosides. MOLECULAR STRUCTURE

gall /GAWL/ (1) in plants, an abnormal outgrowth of tissues; caused by a variety of parasites, ranging from insects to fungi and bacteria; (2) in animals, bile.

gametangium (pl gametangia) /GAM-muh-TAN-jee-uhm/ A compartment in which ferns, mosses, and fungi develop their gametes.

gametes /GAM-eets/  Haploid reproductive cells. Two gametes, one of each sex, fuse during fertilization to produce a zygote during sexual reproduction. A female reproductive cell is an ovum (or egg) and a male reproductive cell is a spermatozoan. MORE INFORMATION

Gametes: Spermatozoan making contact with an ovum

gametic number (N) /guh-MEET-ik/ The haploid number of chromosomes.

gametocyte /guh-MEE-tuh-site/ A cell from which gametes are formed by division (i.e., spermatocyte or oocyte).

gametogenesis /guh-MEE-tuh-GEN-uh-suhs/ The process of gametic development.

gametophyte /guh-MEE-tuh-fite/ A multicellular haploid form, occurring in the life cycle of a plant or fungus undergoing alternation of generations, that produces haploid gametes via mitosis. PICTURE: GAMETOPHYTE OF SCALY MALE-FERN (Dryopteris affinis) | PICTURE: SPOROPHYTE OF SCALY MALE-FERN (Dryopteris affinis)

gamone /GAM-oan/ A hormone, facilitating fertilization, produced by a gamete.

gamopetalous /GAM-uh-PED-uhl-uhs/ Having the petals of the corolla united.

gamophyllous /GAM-uh-FILE-uhs/ Having united leaves.

ganglion /GANG-lee-awn/ A small mass of nervous tissue composed of numerous cell bodies.

gangrene /GANG-reen/ See: necrosis.

GAP Glyceraldehyde-3-phosphate.

GAPDH Glyceraldehyde-3-phosphate dehydrogenase.

gap junction A type of junction between animal cells that allows current or cellular material to pass from one cell to another.

gastric /GAS-trik/ Of or relating to the stomach.

gastroenteritis /GAS-troh-ehnt-uh-RIGHT-uhs/ Inflammation of the stomach and intestines.

gastroliths /GAS-truh-lith/ Stones found in the stomachs of certain reptiles and fish.

Gastropoda /gas-TRAWP-uh-duh/ The mollusk class comprised of the snails and slugs.

Gastrulation<

gastrula /GAST-truhl-luh/ An early stage in the development of an animal embryo during which its shape is restructured by cell migration. The exact process differs in different animals, but in the more complex organisms it typically involves an infolding of the blastula to form a two- or three-layered ball of cells.

gastrulation /GAST-truhl-AY-shun/ The process that forms a gastrula.

gazelle /guh-ZELL/ Any of various small, swift Asiatic or African antelopes.

GC-rich region A region of a chromosome where the base pair G-C occurs at an elevated frequency; often indicates a gene-rich region.

GDP The diphosphate ester of pyrophosphoric acid with the nucleoside guanosine; present in RNA.

gene A unit of hereditary information located on a chromosome, composed of DNA, and specifying a particular product (either a protein or an RNA molecule). See also: gene expression.

gene expression The process by which the information, stored in the DNA of which a gene is composed, is converted into a corresponding RNA or protein molecule that can perform some physiological function.

gene family (also multigene family) A set of genes, presumed descendants of a single ancestral gene, that through duplication of loci and subsequent mutation, has become a related set of genes occurring at different loci.

gene frequency See: Allele frequency.

gene mapping Determination of the location of genes on a chromosome (or plasmid).

gene pool The genetic variation present in a sexually-reproducing population.

gene prediction Computer prediction of possible genes in an unannotated nucleotide sequence.

gene product The product, RNA or protein, produced from a gene. The activity of a gene is measured in terms of the amount of gene product produced by that gene.

gene therapy A procedure that attempts to replace, manipulate, or supplement misfunctioning genes with properly functioning ones. See also: gene, germ line gene therapy, somatic cell gene therapy.

gene transfer Intentional incorporation of foreign DNA into the cells of an organism, usually via a vector (e.g., a genetically engineered virus). Used in gene therapy.

genetic /juh-NET-ik/ (1) having a hereditary basis, as opposed to an environmental cause; (2) of, relating to, produced by, or being a gene or genes.

The Genetic Code

genetic code /juh-NET-ik/ The correspondence between nucleotide triplets in DNA or RNA (codons) and the amino acids in protein (see table at right). A gene's DNA sequence determines the mRNA sequence produced from it, and the genetic code then determines the amino acid sequence in the protein produced from that mRNA. The genetic code is apparently the same in all organisms (with the exception of a few mitochondrial systems).

genetic drift See: random genetic drift.

genetic engineering Altering the genetic material to allow it to perform new functions or make new products.

genetic marker /juh-NET-ik/ (1) a probe used to mark a gene, chromosome, or nucleus; (2) a phenotypic trait indicating the presence of a particular allele.

genetic mosaic /juh-NET-ik moh-ZAY-ik/ An organism in which different cells differ at the genetic level; results either from fusion of embryos or mutation during development.

genetic polymorphism /juh-NET-ik PAWL-ee-MORE-fizz-uhm/ Genetic variation within a population.

genetics /juh-NET-iks/ The study of heredity.

genic /JEE-nik, JEH-/ Of, pertaining to, affecting, or based on genes.

genome /JEE-noam/ An entire virus, plasmid, bacterial chromosome, or haploid set of eukaryotic chromosomes, considered as a single informational unit; more generally, the term is applied to all the chromosomes of an organism, to an entire virus, or to some class of chromosome or plasmid, such as a mitochondrial genome.

genomic library /juh-NOAM-ik/ A set of clones composed of overlapping, randomly generated DNA fragments representing an organism's entire genome.

genomics /juh-NOAM-iks/ The study of entire genomes.

genotype /JEEN-oh-type/ The genetic constitution of an organism, as opposed to its physical appearance (phenotype).

genucubital /JEH-noo-KOOB-uh-tuhl/ Pertaining to the knees and elbows.

genus (pl genera) /JEE-nuhs, je-NAIR-uh/ In taxonomy, a division of a family that itself contains one or more forms treated as species. CHART OF RELATIVE TAXONOMIC RANKS

geobiology A science that combines geology and biology to study the interactions of organisms with their environment.

geology /jee-AWL-uh-jee/ The scientific study of the history of the earth and of its life.

geriatrics /JER-ree-AT-riks/ Medical treatment and study of the diseases of the elderly.

germ (1) a prokaryote; (2) the portion of a seed or grain from which the embryo develops.

germ cell A reproductive cell that combines with another of the opposite sex during fertilization.

germ line Term used to refer to cells that give rise to gametes, and so, to descendant generations.

germ line gene therapy An experimental method of preventing genetic disease, in which genes are inserted into germ cells or zygotes to prevent the disease in offspring.

germ line mutation A heritable mutation.

germination /jer-muh-NAY-shun/ The initial growth of a seed or spore.

gestation /jes-TAY-shun/ The period during which the fetus is developing in the uterus.

gibberellins /JIB-ur-REL-ins/ Plant hormones that stimulate leaf and stem growth. They also bring buds out of dormancy and cause seed germination. In conjunction with auxin, they stimulate fruit production.

Gibbs free energy (ΔG) /GIBZ/ The maximum amount of work that can be carried out by a reaction at constant temperature and pressure. If ΔG is negative, the reaction occurs spontaneously at constant temperature and pressure (if positive, the reverse reaction occurs). Named for the American mathematician J. Willard Gibbs.

gigabase /GIG-uh-BASE/ A measure of nucleotide sequence length equal to one billion base pairs.

gills /GILZ/ Gas-exchange organs found in many aquatic animals.

gingivoglossitis /JIN-juh-vuh-glaws-EYE-tuhs/ Inflammation of the gums and tongue.

Giraffa camelopardalis Scientific name for the giraffe. INTERESTING FACTS ABOUT GIRAFFES | DIET | GIRAFFE HABITAT AND DISTRIBUTION

GLC Gas-liquid chromatography.

Glc Glucose.

GlcN Glucosamine

glial cells /GLEE-uhl/ Cells found in nervous tissue that support the neurons and electrically insulate them by producing myelin.

Gln Glutamine.

glomerulus /gluh-MAIR-yuh-luhs/ A cluster of capillaries, particularly within the Malpighian body of the kidney, where each such cluster is enclosed in an envelope known as Bowman's capsule that filters the compounds excreted in urine out of the blood.

glossalgia /gloss-AL-zhuh/ Pain in the tongue.

glossitis (also glottitus) /glaw-SIGHT-uhs, glawt-TIGHT-uhs/ Inflammation of the tongue.

glossodynia /gloss-oh-DIN-yuh/ Pain in the tongue.

glottis /GLAWT-tuhs/ The sound-producing portion of the larynx; composed of the two vocal folds, or cords, and the space between them.

glottitis See: glossitis.

Glu Glutamic acid.

gluconeogenesis /GLOO-koh-NEE-oh-JEHN-uh-suhs/ A metabolic pathway producing glucose from non-carbohydrate carbon substrates.

glucosamine (GlcN) /glue-KOAS-uh-mean, -KOAZ-/ An amino sugar and a important precursor in the synthesis of glycosylated proteins and lipids. Glucosamine is an abundant monosaccharide is present in the polysaccharide chitin, a major constituent of the cuticles of arthropods and cell walls of fungi. MOLECULAR STRUCTURE

glucose (Glc) /GLOO-cohs/ The most important carbohydrate in body metabolism; used by cells as a source of energy and as a metabolic intermediate. A monosaccharide, it also known as corn or grape sugar (also dextrose). In circulation, it is blood sugar. Glucose is formed during digestion, especially from starch and sucrose. Glucose is an isomer of fructose. Photosynthesis produces glucose and oxygen. MOLECULAR STRUCTURE

glucose-6-phosphate (G6P) Glucose sugar phosphorylated on carbon 6. Represents the first step of glycolysis and the pentose phosphate pathway. Most of the glucose in a cell is phosphorylated in this way upon entry.

glutamic acid (Glu or E) /gloo-TAM-ick/ A nonessential amino acid. CODONS | MOLECULAR STRUCTURE

glutamine (Gln or Q) /GLOOT-uh-meen/ A nonessential amino acid. CODONS | MOLECULAR STRUCTURE | BIOSYNTHESIS

glutathione /glued-uh-THIGH-own/ A tripeptide important as an intracellular antioxidant. It exists in reduced (GSH) and oxidized (GSSG) states. GSH is regenerated from GSSG by glutathione reductase.

Gly Glycine.

glyceraldehyde-3-phosphate (G3P also: GADP, GAP, TP, GALP or PGA) /GLISS-er-ALD-uh-hide/ Present in all organisms, G3P is an intermediate in various important metabolic pathways (e.g, photosynthesis, tryptophan and thiamine biosynthesis). It is a phosphate ester of the 3-carbon sugar glyceraldehyde.

glycerol /GLIS-er-awl/ Glycerol is a precursor of triacylglycerols and of phospholipids. When the body extracts energy from fat, glycerol and fatty acids are released into the blood. In the liver, glycerol is converted to glucose, which provides energy another source of energy for cellular metabolism. MOLECULAR STRUCTURE

glycine (Gly or G) /GLIGH-seen/ The smallest of the 20 amino acids found in proteins. It is nonessential in the human diet because it is produced in the body from serine. CODONS | MOLECULAR STRUCTURE

glycocalyx /GLIGH-ko-KAY-licks/ A rough coat of adhesive oligosaccharides on the external surface of animal cells.

glycogen /GLIGH-kuh-jehn/ Polysaccharide that serves the same energy-storing function in animals that starch does in plants.

glycolysis /gligh-KALL-luh-suhs/ The production of pyruvic acid by the splitting of glucose. It is the single metabolic pathway occurring in all types of living cells. One molecule of glucose breaks down into two molecules of pyruvate. The pyruvate molecules provide energy to two main ways: They are converted into (1) acetyl-coenzyme A, the main input for the Krebs cycle; and (2) oxaloacetate, which re-energizes Krebs cycle intermediates (oxaloacetate also plays a role in gluconeogenesis). SEE DIAGRAM OF GLYCOLYSIS

glycoprotein /GLIGH-koh-PRO-teen/ A protein containing oligosaccharide chains covalently bonded topolypeptide side-chains. The process of attaching these oligosaccharides is known as glycosylation.

glycosylation /gligh-KOS-suh-lay-shun/ Glycoprotein.

GMP Guanosine monophosphate.

Golgi apparatus (also Golgi complex and Golgi body) /GOHL-jee/ An organelle in eukaryotic cells; it stores, guides, and modifies the products of the endoplasmic reticulum.

gonadotropins /guh-NAHD-uh-TROPE-uhns/ Those hormones playing a role in the development and activation of the sex glands (testes and ovaries).

gonads /GO-nads/ Sex glands (of either sex).

Gondwana /gond-WAWN-uh/ A former supercontinent from which are derived the modern continents of Australia, South America, Africa, and Antarctica, as well as Madagascar, India, and New Zealand. It existed from the Cambrian Period to the Jurassic and began breaking up during the Triassic.

gonium /GOAN-ee-uhm/ An undifferentiated germ cll.

gonopoietic /GAWN-uh-poy-EHT-ik/ Producing gametes.

gonotome /GAWN-uh-tome/ The portion of a somite that develops into the genitals.

Gorgonacea /gore-guh-NAWSH-ee-uh/ The echinoderm order including gorgonians, sea fans, and sea feathers.

gradualist An adherent of the tradition of thought maintaining that evolution is a gradual process (see gradualism).

gradualism (also gradualistic evolution) The assertion that during the course of evolution new forms of life typically come into being via gradual, continuous processes; used in opposition to the term saltatory evolution. More information.

graft (1) to transfer a part of an organism either to some other part of the same organism (autograft), or to some other organism; (2) the part so transferred.

graft hybrid /HIGH-brid/ A plant, composed of a host -- the lower, rooted portion — together with an upper grafted portion derived from some individual other than the host (donor).

grain (gr.) A measure of weight (= 0.065 gram) used in pharmacology.

granum (pl grana) /GRAY-nuhm, GRAN-uhm, GRAW-num/ One of the stacks of thylakoids within a chloroplast that convert light into chemical energy.

gravid /GRAV-id/ (1) pregnant; (2) swollen with embryos or eggs.

gravitropism /GRAV-uh-TROPE-iz-uhm/ A gravity-stimulated response in an animal or plant.

grazer An animal that feeds on grass and low-growing herbage.

greenhouse effect Planetary warming due to accumulation of certain gases in the atmosphere. The major greenhouse gases are methane, carbon dioxide, nitrous oxide, and three types of fluorinated gases (sulfur hexafluoride, PFCs, and HFCs)

GS Glutamine synthetase.

GSH (reduced) Glutathione.

GSSG Glutathione disulfide (oxidized glutathione).

GTP Guanosine triphosphate.

Guanosine /GWAN-uh-seen/ See: nucleoside.

Guanosine monophosphate (GMP) /GWAN-uh-seen/ A monophosphate ester of phosphoric acid with the nucleoside guanosine. GMP is composed of a ribose, phosphate group attached to the carbon C5' of the ribose, and guanine attached to the carbon C1'.

Guanosine triphosphate (GTP) /GWAN-uh-seen/ A purine nucleotide present in RNA. It has a ribose sugar and three phosphates, with guanine attached to carbon C1' and the triphosphate attached to carbon C5'. GTP is used as a energy source in various metabolic reactions (like ATP).

guard cells Epidermal cells that rim the stomata of plants.

Comparison of gymnosperm seed with that of an angiosperm (click to enlarge)

gymnosperms /JIM-noh-sperms/ Vascular plants bearing naked seeds.

gynandromorphs /guy-NAND-ruh-morphs/ Organisms that have both male and female cells.

gynecology /GUY-nuh-KALL-uh-jee/ The study and medical treatment of the diseases of women, in particular those affecting the genitals and urinary tract.

gynoecium (or gynecium) /guy-NEESH-uhm/ All of the carpels of a flower taken together.

gyrus (pl gyri). /JIGH-ruhs/ One of the convolutions of the brain.