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G protein |
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. |
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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. |
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G1 phase |
The first growth phase of the cell cycle, consisting of the portion of interphase before DNA synthesis begins. |
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G2 phase |
The second growth phase of the cell cycle, consisting of the portion of interphase after DNA synthesis occurs. |
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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. |
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gamete (gam-eet) [Gk., wife] |
A haploid egg or sperm cell; gametes unite during sexual reproduction to produce a diploid zygote. |
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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. |
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ganglion (gang-lee-un) pl. ganglia (gang-lee-on) [Gk. ganglion, a swelling] |
A cluster (functional group) of nerve cell bodies in a centralized nervous system. |
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gap junction |
A type of intercellular junction in animal cells that allows the passage of material or current between cells. |
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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. |
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gastric [Gk. gaster, stomach] |
Pertaining to the stomach. |
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gastrin |
A digestive hormone, secreted by the stomach, that stimulates the secretion of gastric juice. |
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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. |
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gastrula (gas-troo-la) [Gk. gaster, stomach] |
The two-layered, cup-shaped embryonic stage. |
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gastrulation (gas-truh-lay-shun) |
The formation of a gastrula from a blastula. |
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gated ion channel |
A specific ion channel that opens and closes to allow the cell to alter its membrane potential. |
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Gause's principle |
See Competitive exclusion. |
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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. |
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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). |
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gene amplification |
The selective synthesis of DNA, which results in multiple copies of a single gene, thereby enhancing expression. |
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gene cloning |
The production of multiple copies of a gene. |
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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. |
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gene pool |
The total aggregate of genes in a population at any one time. |
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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. |
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genetic drift |
Changes in the gene pool of a small population due to chance. |
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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. |
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genetic map |
An ordered list of genetic loci (genes or other genetic markers) along a chromosome. |
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genetic recombination |
The general term for the production of offspring that combine traits of the two parents. |
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genome (jee-nome) |
The complete complement of an organism's genes; an organism's genetic material. |
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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. |
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genomic library |
A set of thousands of DNA segments from a genome, each carried by a plasmid, phage, or other cloning vector. |
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genotype (jee-noh-type) |
The genetic makeup of an organism. |
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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. |
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geographical range |
The geographic area in which a population lives. |
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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. |
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germ cells [L. germinare, to bud] |
Gametes or the cells that give rise to gametes |
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germination [L. germinare, to bud] |
In plants, the resumption of growth or the development from seed or spore. |
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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. |
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gill |
A localized extension of the body surface of many aquatic animals, specialized for gas exchange. |
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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. |
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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. |
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globular protein [L. dim. of globus, a ball] |
A polypeptide chain folded into a roughly spherical shape. |
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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. |
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glucagon [Gk. glykys, sweet + ag |
A peptide hormone secreted by pancreatic endocrine cells that raises blood glucose levels; an antagonistic hormone to insulin. |
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glucocorticoid |
A corticosteroid hormone secreted by the adrenal cortex that influences glucose metabolism and immune function. |
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glucose [Gk. glykys, sweet] |
A six-carbon sugar (C6H12O6); the most common monosaccharide in animals. |
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glycerol |
A three-carbon molecule with three hydroxyl (![]() |
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glycocalyx (gly-koh-kay-liks) |
A fuzzy coat on the outside of animal cells, made of sticky oligosaccharides. |
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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. |
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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. |
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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. |
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glycoprotein [Gk. glykys, sweet + proteios, primary] |
A protein with covalently attached carbohydrate. |
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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. |
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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. |
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gonads [Gk. gone, seed] |
The male and female sex organs; the gamete-producing organs in most animals. |
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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. |
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gradualism |
A view of Earth's history that attributes profound change to the cumulative product of slow but continuous processes. |
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Gram stain |
A staining method that distinguishes between two different kinds of bacterial cell walls. |
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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. |
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gravitropism (grav-eh-troh-piz-um) [L. gravis, heavy + Gk. trope, turning] |
A response of a plant or animal in relation to gravity. |
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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. |
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gross primary productivity (GPP) |
The total primary productivity of an ecosystem. |
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gross productivity |
A measure of the rate at which energy is assimilated by the organisms in a trophic level, a community, or an ecosystem. |
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ground meristem [Gk. merizein, to divide] |
A primary meristem that gives rise to ground tissue in plants. |
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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. |
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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. |
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guard cell |
A specialized epidermal plant cell that forms the boundaries of the stomata. |
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guttation |
The exudation of water droplets caused by root pressure in certain plants. |
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gymnosperm (jim-noh-spurm) [Gk. gymnos, naked + sperma, seed] |
A vascular plant that bears naked seeds not enclosed in any specialized chambers. |
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A B C D E F G H I J K L M N O P Q R S T U V W X Y Z |
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Glossary from Biology, Fifth Edition By Campbell, Reece, Mitchell © 1998, Benjamin Cummings. Reprinted with Permission. All Rights Reserved |