human immune system to fuse (causing collapse of the immune system). See also

ACQUIRED IMMUNE DEFICIENCY SYNDROME

(AIDS), HUMAN IMMUNODEFICIENCY VIRUS TYPE 1

(HIV- 1), HUMAN IMMUNODEFICIENCY VIRUS TYPE 2 (HIV- 2), HELPER T CELLS (T4 CELLS),

ADHESION MOLECULE.

Futile Cycle An enzyme-catalyzed set of cyclic reactions that results in release of thermal energy (heat) through the hydrolysis of ATP

(adenosine triphosphate). The hydrolysis of ATP is normally coupled to other cycles and reactions in which the energy released is metabolically used. However, futile cycles would appear to waste the energy of ATP as heat, except when one is shivering to keep warm. The production of heat by shivering is an example of the futile cycle. See also

ADENOSINE TRIPHOSPHATE (ATP), ENZYME,

HYDROLYSIS.

F

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G

G- See GRAM-NEGATIVE (G- ).

G+ See GRAM-POSITIVE (G+).

G-Protein-coupled Receptors See G-PROTEINS. G Proteins See G-PROTEINS.

G-Proteins (Guanyl-Nucleotide Binding Proteins) Discovered by Rodbell and co-workers at America’s National Institutes of Health (NIH), and Alfred G. Gilman and co-workers at the American University of Virginia-Char- lottesville, during the 1970s–1980s. These are proteins embedded in the surface membrane of cells. G-proteins “receive chemical signals” from outside the cell (e.g., hormones) and “pass the signal” into the cell, so that cell can “respond to the signal.” For example, a hormone, drug, neurotransmitter, or other “signal” binds to a receptor molecule on the surface of the cell’s exterior membrane. That receptor then activates the G-protein, which causes an effector inside cell to produce a second “signal” chemical inside the cell, which causes the cell to react to the original external chemical signal. The G-proteins are called thus, because they become GTP and GDP forms alternately, as part of their reaction cycle (i.e., in “passing the signal”). Dysfunction of G-proteins in humans causes the salt and water losses inherent in cholera (the body’s compromised immune defense inherent in pertussis), and is believed responsible for some symptoms of diabetes and alcoholism. Dysfunction of G-proteins in plants causes rapid water loss (wilting). See also

PROTEIN, SIGNALING, SIGNAL TRANSDUCTION, HOR-

MONE, CELL, BETA CELLS, GTPases, GPA1, INSULIN,

RECEPTORS, NATIONAL INSTITUTES OF HEALTH

(NIH), NEUROTRANSMITTERS, TRANSMEMBRANE

PROTEINS, ION CHANNELS, CHOLERA TOXIN.

GA21 A naturally occurring gene (i.e., expressed at low levels in some plants)

0-8493-XXXX-X/01/$0.00+$1.50 © 2001 by CRC Press LLC

	which confers resistance to glyphosate-con-
	taining herbicides. When the GA21 gene is
	inserted by man into crop plants (e.g.,
	maize/corn) in a way that causes high
	expression, those crop plants are subse-
		G
	quently unaffected when glyphosate-con-
	taining herbicides are applied to fields to
	cotnrol weeds in those crops. See also GENE,
	EXPRESS, EXPRESSIVITY, PROTEIN, GENETIC ENGI-
	NEERING, CORN, HERBICIDE-TOLERANT CROP,
	GLYPHOSATE.
	Galactose (gal) A monosaccharide occurring
	in both levo (L) and dextro (D) forms as a
	constituent of plant and animal oligosaccha-
	rides (lactose and raffinose) and polysaccha-
	rides (agar and pectin). Galactose is also
	known as cerebrose. See also STEREOISOMERS,
	DEXTROROTARY (D) ISOMER, LEVOROTARY (L)
	ISOMER.
	Gall See Ti PLASMID.
	GalNAc N-acetyl-D-galactosamine.
	GALT See GUT-ASSOCIATED LYMPHOID TISSUE.
	Gamete A germ or reproductive cell. In ani-
	mals (and humans) the functional, mature,
	male gamete is called a spermatozoon; in
	plants it is called a spermatozoid. In both
	animals and plants the female gamete is
	called the ovum, or egg. See also OOCYTES.
	Gamma Globulin A type of blood protein that
	plays a major role in the process of immunity
	(immune system response). Sometimes the
	term “gamma globulin” refers to a whole
	group of blood proteins that are known as
	antibodies or immunoglobulins (Ig). Most
	often, however, it applies to a particular
	immunoglobulin, designated as IgG,
	believed to be the most abundant type of
	antibody in the body. See also ANTIBODY,
	G GUT -ASSOCIATED LYMPHOID TISSUE (GALT),
	PROTEIN, IMMUNOGLOBULIN.

© 2002 by CRC Press LLC

Gamma Interferon Produced by T lympho-

cytes. See also INTERFERONS, T LYMPHOCYTES.

GAP A double-stranded DNA is said to be “gapped” when one strand is missing over a short region of the molecule. See also DEOXY-

RIBONUCLEIC ACID (DNA).

Gated Transport (of a protein) One of three means for a protein molecule to pass between compartments within eucaryotic cells. The compartment “wall” (membrane) possesses a “sensor” (receptor) that detects the presence of a correct protein (e.g., after

Gthat protein has been synthesized in the cell’s ribosomes), then opens a “gate” (pore) in the membrane to allow that protein to pass from the first compartment to the second compart-

ment. See also PROTEIN, EUCARYOTE, CELL,

RIBOSOMES, SIGNALING, VESICULAR TRANSPORT.

GDH Gene See GLUTAMATE DEHYDROGENASE.

GDNF See GLIAL DERIVED NEUROTROPHIC FACTOR.

GEAC The country of India’s Genetic Engineering Approval Committee. The GEAC must approve a rDNA product (e.g., a genetically engineered crop plant that earlier received its “bio safety clearance” from the Indian Department of Biotechnology) before that rDNA product is allowed to be commercially planted. See also GENETIC ENGINEERING,

rDNA, INDIAN DEPARTMENT OF BIOTECHNOLOGY.

Gel A colloid, where the dispersed phase is liquid and the dispersion medium is solid.

Gel Electrophoresis See TWO-DIMENSIONAL (2D)

GEL ELECTROPHORESIS, POLYACRYLAMIDE GEL

ELECTROPHORESIS (PAGE), ELECTROPHORESIS.

Gel Filtration Also known as exclusion chromatography. An effective technique for separating molecules (such as peptide mixtures) on the basis of size. This is accomplished by passing a solution of the molecules to be separated over a column of Sephadex®, for example, which is a polymerized carbohydrate derivative that contains tiny holes. The holes are of such a size that some of the smaller molecules diffuse into them and are in this way retained (held back) while the larger molecules are not able to get into the holes and pass on by the solid phase (Sephadex®, in this example). This, simplistically, is how separation is effected. See also

ELECTROPHORESIS, CHROMATOGRAPHY, FIELD

INVERSION GEL ELECTROPHORESIS.

GEM (Germ plasm Enhancement for Maize) A project conducted under the auspices of the U.S. Department of Agriculture, in concert with 16 American universities and 20 corn (maize) seed companies. GEM’s intent is to cross exotic (not in current use) germ plasm with commercial maize lines in order to increase corn yield. See also CORN,

GERM PLASM, HYBRIDIZATION (PLANT GENETICS),

PLEIOTROPIC.

GEMP (Genetically Engineered Microbial

Pesticide) See GENETICALLY ENGINEERED

MICROBIAL PESTICIDE, INTEGRATED PEST MAN-

AGEMENT (IPM).

Gene A natural unit of the hereditary material, which is the physical basis for the transmission of the characteristics of living organisms from one generation to another. The basic genetic material is fundamentally the same in all living organisms: it consists of chainlike molecules of nucleic acids — deoxyribonucleic acid (DNA) in most organisms and ribonucleic acid (RNA) in certain viruses — and is usually associated in a linear arrangement that (in part) constitutes a chromosome.

The segment of DNA that is involved in producing a polypeptide chain. It includes regions preceding and following the coding region (leader and trailer) as well as intervening sequences (introns) between individual coding segments (exons). More than one protein can be expressed (made) from a given gene (i.e., the particular protein expressed is determined by factors such as the cell’s temperature or other environmental variable, or the presence of STATs, some of which themselves are proteins). See also

INFORMATIONAL MOLECULES, DEOXYRIBO-

NUCLEIC ACID (DNA), RIBONUCLEIC ACID (RNA),

GENE EXPRESSION, CHROMOSOMES, EXPRESS,

MESSENGER RNA (mRNA), CODON, INTRON, EXON,

CODING SEQUENCE, GENE EXPRESSION CASCADE,

CENTRAL DOGMA (NEW), SIGNAL TRANSDUCERS

AND ACTIVATORS OF TRANSCRIPTION (STATs).

Gene “Stacking” See “STACKED” GENES.

Gene Amplification The copying of segments (e.g., genes) within the DNA or RNA molecule. This can be done by man (e.g.,

© 2002 by CRC Press LLC

polymerase chain reaction), can be caused by certain chemical carcinogens (e.g., phorbol ester), or occur naturally (e.g., in procaryotes and certain lower eucaryotes). The five primary techniques used by man to perform gene amplification are:

1.Polymerase Chain Reaction (PCR)

2.Ligase Chain Reaction (LCR)

3.Self-sustained Sequence Replication (SSR)

4.Q-beta Replicase Technique

5.Strand Displacement Amplification (SDA)

See also GENE, Q-BETA REPLICASE TECHNIQUE,

POLYMERASE CHAIN REACTION (PCR), CARCINOGEN,

PROCARYOTE, EUCARYOTE.

Gene Array Systems See BIOCHIPS, PROTEOM-

ICS, GENE EXPRESSION ANALYSIS.

Gene Chips See BIOCHIPS, GENE EXPRESSION

ANALYSIS, PROTEOMICS.

Gene Delivery (gene therapy) The insertion of genes (e.g., via retroviral vectors) into selected cells in the body in order to:

1.cause those cells to produce specific therapeutic agents (growth hormone in livestock, factor VIII in hemophiliacs, insulin in diabetics, etc.). A potential way of curing some genetic diseases, in that the inserted gene will produce the protein and/or enzyme that is missing in the body due to a defective gene (thus causing the genetic disease). Approximately 3,000 genetic diseases are known to man. Examples of genetic diseases include cystic fibrosis, sickle cell anemia, Huntington’s disease, phenylketonuria (PKU), Tay-Sach’s disease, ADA deficiency (adenosine deaminase enzyme deficiency), and thalassemia.

2.cause those cells to become (more) susceptible to a conventional therapeu-

tic agent that previously was ineffec- t i v e a g a i n s t t h a t p a r t i c u l a r condition/disease (e.g., insertion of Hstk gene into brain tumor cells to make those tumor cells susceptible to the Syntex drug Ganciclovir).

3.cause those cells to become less susceptible to a conventional therapeutic agent (e.g., insert genes into healthy tissue in order to enable that healthy tissue to resist the harmful effects of such conventional chemotherapy agents as vincristine).

4.counter the effects of abnormal (damaged) tumor suppressor genes via insertion of normal tumor suppressor genes.

5.cause expression of ribozymes that cleave oncogenes (cancer-causing

genes).	G
6. be used for other therapeutic uses of
genes in cells.
See also TUMOR SUPPRESSOR GENES, ONCOGENES,
CANCER, p53 GENE, TUMOR, PROTO-ONCOGENES,
RETROVIRAL VECTORS, RETROVIRUSES, HUNTING-
TON’S DISEASE, GENETIC CODE, INFORMATIONAL
MOLECULES, DEOXYRIBONUCLEIC ACID (DNA),
CHROMOSOMES, HORMONE, ENZYME, PROTEIN,
GENETIC TARGETING.
Gene Expression Conversion of the genetic
information within a gene, into an actual
protein (or cell process). Note that many
genes are only expressed at specific times
during the lifetime of an organism. Some
genes are expressed in a “cascade” of related
expressions. See also GENE, GENETIC CODE,
INFORMATIONAL MOLECULES, EXPRESS, GENE

EXPRESSION ANALYSIS, BIOCHIPS, GENE EXPRES-

SION CASCADE, CENTRAL DOGMA (NEW).

Gene Expression Analysis Generally done via use of “biochips” (which have numerous detection/analysis devices fabricated onto their silicon surface) or “microarrays,” gene expression analysis involves evaluation of the expression (and expression levels) of numerous genes in a biological sample, to analyze/compare any differences between gene expression/products in:

1.Normal cells vs. diseased cells.

2.Normal cells vs. those responding to a stimulus.

3.Cells from the same organism, at different stages of development (e.g., embryo versus adult).

© 2002 by CRC Press LLC