Galactose: Obtained from milk sugar by enzymatic action or boiling with a mineral acid. It is less sweet than table sugar. Gallbladder: A digestive organ, which stores bile (produced in the liver), used in the digestion and absorption of fats in the duodenum. Gallstone: A solid mass, usually of cholesterol, formed in the gallbladder or bile duct. Gametogenesis: Formation of gametes (ova and sperm). This process is called meiosis when a germ cell containing full complement of chromosomes divides to produce mature sex cells containing half the number of chromosomes. Gamma-interferon: The major interferon produced by immunologically stimulated lymphocytes primarily the T lymphocytes. Ganglioside: A general designation for a member of a class of galactose containing lipid found in the tissue of the central nervous system. Gastritis: Inflammation of the stomach. Gastrointestinal stromal tumor: GIST. A type of tumor that usually develops in cells in the wall of the gastrointestinal tract. It can be benign or malignant. Malignant GISTs can occur anywhere from the esophagus to the rectum, but occur most commonly in the stomach and small intestine. Treatment for GIST includes STI571 (Gleevec), the first approved drug to directly turn off the signal of a protein known to cause a cancer. Gelatinases: Proteolytic enzymes, which hydrolyzes gelatin. Gene: A stretch of DNA in a chromosome that codes for a functional product, RNA or protein. Gene Expression: The transfer of information encoded in a gene into protein or RNA. Gene expression includes transcription of DNA into mRNA and then translation into protein. It also includes transcription to other RNAs such as transfer RNA (tRNA) and ribosomal RNA (rRNA) that are not translated into protein. Gene Product: Macromolecules produced from a gene such as RNA and eventually proteins. Gene Transcription: Synthesis of RNA by RNA polymerases using a DNA template. Genetic code: The dictionary of triplet sequences in mRNA (triplet codons) which defines the sequence of amino acids in a protein. Genetic Engineering: Technique to manipulate genetic material. Genetic Polymorphism: The occurrence together in the same population of two or more genetically determined phenotypes in such proportions that the rarest of them cannot be maintained merely by recurrent mutations. Genetic segregation: Separation of allelic genes during meiosis (a special method of cell division of matured sex cells) as homologous chromosomes begin to migrate toward the poles of the cell, so that eventually the members of each pair of allelic genes go to separate gametes (haploid reproductive cells ova or spermatozoa). Genome: The total set of genes carried by an individual or cell. Genomic DNA: DNA present in the genome, the genetic material in an organism. Germ cells: Cells that produce sperm and ovum. These cells transmit genetic information from one generation to another. Germ line: Cells which differentiate very early in the formation of the embryo and later exclusively undergo a special kind of reduction cell division to produce the sex cells ova and sperm. Mature sex cells have half the number of chromosome as the somatic cells. Glioblastoma multiforme: An astrocytoma of grade III or IV; it is a rapidly growing tumor consisting of a mixture of cells. Glioblastoma: A general term for malignant tumor of some type of nerve cell. Glioma: A tumor composed of tissue which represents supporting structure of nervous tissue (neuroglia). The term is sometimes extended to include all the primary intrinsic malignancy of the brain and spinal cord. Globulin: A class of proteins, which are not soluble in water but soluble in salt solution Glucan: One of a group of polysaccharide sugars composed of D-glucose monomers linked together by glycosidic bonds. Examples of glucans are dextran, laminarin, and lichenin. Glucagon: A polypeptide hormone secreted by the alpha cells of the islets of Langerhans in pancreas in response to low blood sugar or stimulation by growth hormone. Glucocorticoid: A group of corticosteroids (containing 21 carbons) predominantly affecting carbohydrate metabolism. They also have other effects including effect on fat and protein metabolism. Gluconeogenesis: The formation of glucose from molecules that are not themselves carbohydrates, as from amino acids, lactate, and the glycerol portion of fats. Glucose: A monosaccharide (hexose), C6H12O6, found in certain foodstuffs, especially fruits and in the normal blood of all animals. It is the end product of carbohydrate metabolism and is the chief source of energy for living organisms, its utilization being controlled by insulin. Glutamic Acid: One of the 20 amino acids commonly found in proteins. Plays a central role in amino acid metabolism, acting as precursor of glutamine, proline and arginine. Also acts as amino group donor in the synthesis by transamination of alanine from pyruvate and aspartic acid from oxaloacetate. Glutamate is also a neurotransmitter, the product of its decarboxylation is the inhibitory neurotransmitter amino butyrate (GABA). Glutathione S-transferase: Enzyme involved in the detoxification of many compounds has high affinity for glutathione, a sulfur containing tripeptide. Glutathione: A tripeptide composed of the amino acids glutamate, cysteine and glycine. It is widely distributed in animal and plant tissues and functions in various reactions in the destruction of peroxides and free radicals. Glycerol: A sugar alcohol, being the alcoholic component of the fats. It is soluble in water and alcohol. Glycerol is an intermediate in the metabolism of fatty acids and serves as phosphate acceptor. Glycogen: A long-chain polymer of glucose, formed in and largely stored in liver and acts as carbohydrate storage in animals. It can be depolymerized by enzyme and liberated as glucose when needed. Glycolipid: A lipid containing carbohydrate groups. Glycolysis: The anaerobic enzymatic conversion of glucose to the simpler compounds lactate, or pyruvate, resulting in energy stored in the form of adenosine triphosphate (ATP). Glycoprotein: Proteins where sugar molecules are attached. Glycosylase: Enzyme that breaks the linkage containing glycosyl (carbohydrate) group. Glycosylated protein: Protein that is linked to carbohydrate moiety. Glycosylation: Formation of linkages with glycosyl, a radical derived from carbohydrate, group. GM-CSF: Granulocyte-macrophage colony-stimulating factor can be produced by a broad range of normal cells such as macrophages, bone marrow cells, and T cells under mitogenic, antigenic or other kinds of stimulating signals. The GM-CSF thus produced stimulates the formation of granulocytes and macrophages. Gn-RH: A dipeptide hormone produced by the hypothalamus that stimulates the release of follicle-stimulating hormone and luteinizing hormone from the anterior lobe of the pituitary gland. Goiter: An enlargement of the thyroid gland, causing swelling of the front part of the neck. This hypertrophy of the gland is due to an effort by pituitary gland to compensate for a deficiency of thyroid hormone production, for example by inadequate iodine in diet. Goiter patients rarely show clinical hypothyroidism. There are various types of goiter such as nodular, follicular, and vascular. Golgi apparatus: Membranous structure containing a number of flattened sacs with associated vacuoles and vesicles. In this structure further modifications of protein and carbohydrate takes place. Gonadotropin: Any hormone having a stimulating effect on gonads (ovary or testis). Two such hormones are secreted by the anterior pituitary: follicle stimulating hormone and luteinizing hormone. G-protein: Regulatory proteins found in all cells. They are versatile molecular switches, involved in the control of a wide range of biological processes – protein synthesis, signal transduction pathways, growth and differentiation. They all act through a common molecular mechanism based on their ability to bind the guanine nucleotides GTP and GDP selectively and with high affinity. Grading: Histological evaluation of the microscopic structure of tissues to determine the extent of disease, usually used in connection to malignant growth. Graft-versus-host disease: Disease caused by immune response of histoincompatible, immunocompetent donor cells against the tissues of immunoincompetent host. Gram-negative Bacteria: Bacteria that lose stain or decolorize by alcohol after staining with Gram’s method due to presence of thin cell layer. Gram-positive Bacteria: Bacteria that retain stain or resist decolorization by alcohol in Gram’s method of staining. Granulocyte-macrophage colony-stimulating factor (GM-CSF): This factor can be produced by a broad range of normal cells such as macrophages, bone marrow cells, T cells under mitogenic, antigenic or other kinds of stimulating signals. The GM-CSF thus produced stimulates the formation of granulocytes and macrophages. Granulocytes: Any cell containing granules, especially a leukocyte containing neutrophil (stain with neutral dyes), basophil (stain with basic dyes), or eosinophil (stain with the dye eosin) in its cytoplasm. Granulocytopenia: A symptom complex characterized by marked decrease in the number of granulocytes (white blood cells containing granules such as neutrophils, basophils, and eosinophils). Granulosa cell: A cell of the membrana granulosa lining the vesicular ovarian follicle that becomes a luteal cell of the corpus luteum after ovulation. Growth Factor: Protein factors that participate in stimulation of cell division and growth. Gynecologic: Pertaining to female reproductive tract. Gynecomastia: An excessive development of the male mammary glands, even to the functional state.