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.