Glueck Vgluk\, Sheldon; and Glueck, Eleanor orig. Eleanor Touroff (respectively b. Aug. 15, 1896, Warsaw—d. March 10, 1980, Cambridge, Mass., U.S.; b. April 12, 1898, Brooklyn, N.Y., U.S.—d. Sept. 25, 1972, Cambridge, Mass.) U.S. criminologists. Sheldon Glueck immi¬ grated to the U.S. from Poland as a child. He married Eleanor Touroff in 1922. As researchers at Harvard Law School, they studied the careers of criminals and juvenile delinquents and are especially known for the Gluecks’ Social Prediction Tables, which attempted to identify potential delinquents at age six or even younger. See delinquency.
glutamic acid \glu-'ta-mik\ One of the nonessential amino acids, closely related to glutamine. The two constitute a substantial fraction of the amino acids in many proteins (10-20% in many cases and up to 45% in some plant proteins). An important metabolic intermediate as well as a neu¬ rotransmitter molecule in the central nervous system, glutamic acid finds uses in medicine and biochemical research. Its sodium salt is the food flavour enhancer monosodium glutamate (MSG).
glutamine \'glu-t3-,men\ One of the nonessential amino acids, closely related to glutamic acid. It is especially important in the cellular metabo¬ lism of animals as the only amino acid capable of readily crossing the blood-brain barrier. It is used in medicine and biochemical research and as a feed additive.
gluten Mixture of proteins not readily soluble in water that occurs in wheat and most other cereal grains. Its presence in flour makes produc¬ tion of leavened baked goods (see baking) possible because the chainlike gluten molecules form an elastic network that traps carbon dioxide gas and expands with it. The properties of gluten vary with its composition, which differs according to the source. Thus, doughs range from soft and exten¬ sible to tough and elastic, depending on the gluten in the flours. Persons with an allergy to gluten can often eat rice or spelt products.
glycerol Ygli-ss-.roA or glycerin Clear, colourless, viscous, sweet¬ tasting liquid organic compound of the alcohol family, chemical formula HOCH 2 CHOHCH 2 OH. With three hydroxyl (—OH) groups, it can form three types of esters (monoglycerides, diglycerides, and triglycerides). Mono- and diglycerides are common food additives. Fats and oils are triglycerides; their processing into soap was the chief source of glycerol until the mid-20th century, when industrial synthesis took over. Glycerol has thousands of uses, including as an emulsifier, softening agent, plas¬ ticizer, and stabilizer in baked goods, ice cream, and tobacco; in skin lotions, mouthwashes, and cough medicines; as a protective medium for freezing red blood cells, sperm, corneas, and other tissues; in printing inks and in the gums and resins in paints and coatings; in antifreeze mixtures; as a nutrient in fermentation; and as a raw material for nitroglycerin.
glyceryl trinitrate See nitroglycerin
glycine Ygll-.senV One of the nonessential amino acids. The simplest amino acid (NH 2 CH 2 COOH), it occurs in many proteins; especially rich sources are silk fibroin and gelatin. It has a sweet taste and is used to reduce the bitter flavour of saccharin. Other uses are in organic synthesis and biochemical research, as a nutrient and feed additive, and to retard rancidity in animal and vegetable fats.
glycogen Vgll-k3-jan\ Principal storage carbohydrate of animals, occur¬ ring primarily in the liver and resting muscles. It is also found in various bacteria, fungi, and yeasts. Glycogen is a branched polysaccharide, a long chain of glucose units, into which it is broken down when energy is needed.
glycogen storage disease or glycogenosis Ygll-ko-jo-'no-sosV Any of numerous types of hereditary enzyme deficiency resulting in altered metabolism of glycogen. The problems are classified in two groups, those affecting the liver and those involving striated muscle, both primary gly¬ cogen storage sites. Symptoms in the liver group range from symptom¬ atic hypoglycemia with ketosis to asymptomatic liver enlargement (hepatomegaly). In the muscle group, they range from weakness and cramps to fatal heart enlargement.
glycogenosis See glycogen storage disease
glycol Vgll-.kolN Any of a class of organic compounds of the alcohol family in which two hydroxyl groups (—OH; see functional group) are
© 2006 Encyclopaedia Britannica, Inc.
glycolysis ► go I 771
attached to different carbon atoms. The term is often used for the simplest of the class, ethylene glycol (1,2-ethanediol). Propylene glycol (1,2- propanediol), much like ethylene glycol but not toxic, is used extensively in foods, cosmetics, and oral hygiene products as a solvent, preservative, and moisture-retaining agent. Other important glycols include 1,3- butanediol and 1,4-butanediol, used as raw materials for plastics and other chemicals; 2-ethyl-1,3-hexanediol, an insect repellent; and 2-methyl-2- propyl-1,3-propanediol, the raw material of the tranquilizer meprobamate.
glycolysis \gli-'ka-b-s9s\ or glycolytic pathway or Embden- Meyerhof-Parnas pathway \ , em-d3n- , mI-3r- l hof- , par-nos\ Sequence of 10 chemical reactions taking place in most cells that breaks down glucose, releasing energy that is then captured and stored in ATP. One molecule of glucose (plus coenzymes and inorganic phosphate) makes two molecules of pyruvate (or pyruvic acid) and two molecules of ATP. The pyruvate enters into the tricarboxylic acid cycle if enough oxygen is present or is fermented into lactic acid or ethanol if not. Thus, glycolysis produces both ATP for cellular energy requirements and building blocks for synthesis of other cellular products. See also Gustav Georg Embden, Otto Meyerhof.
glycoside \ , glI-ko- l sId\ Any of a wide variety of naturally occurring organic compounds in which a carbohydrate portion consisting of one or more sugars or sugar derivatives is combined with a hydroxy compound (a compound containing an —OH group). Since sugars themselves are hydroxy compounds, polysaccharides are glycosides by definition. Other glycosides include various flower and fruit pigments, several antibiotics (e.g., streptomycin), and the cardiac glycosides (see digitalis).
GM See General Motors Corp.
Gnadenhutten Massacre Vjo-'na-don-.ho-tonX (March 8, 1782) Mur¬ der of 96 Indians, mostly Delawares, by American troops at an Ohio vil¬ lage during the American Revolution. The Indians, converted peaceful Christians, were under suspicion because of their neutrality in the war. An American officer, David Williamson, and his militia, seeking revenge for Indian raids on frontier settlements, pretended friendship with the Indi¬ ans, then disarmed them and returned to kill them in cold blood; two scalped boys escaped to relate the slayings.
Gnam-ri-srong-brtsan N'nam-'re-'sroq-bort-'sanV (b. c. 570—d. c. 619) Descendant of a line of rulers of Yarlong, united tribes in central and southern Tibet that became known to China’s Sui dynasty (581-618). After his assassination, he was succeeded by his son, Srong-brtsan-sgam-po (c. 608-650), who continued his father’s military expansion and established his capital at Lhasa. Srong-brtsan-sgam-po became so powerful that the Tang dynasty (618-907) entered into a marriage alliance with him in 641.
gnat Any member of several species of small dipterans, most of which bite or annoy humans. Midges are also sometimes called gnats. In North America the name is also applied to the blackfly, fruit fly, and other small flies that hover about the eyes of humans and other animals.
gnatcatcher Any of about 11 species of small songbirds (genus Poliop- tila) often treated as a subfamily of the Old World warbler family Sylvi- idae. The blue-gray gnatcatcher, 4.5 in. (11 cm) long, with its long white- edged tail, looks like a tiny mocking¬ bird. It breeds locally from eastern Canada and California to the Baha¬ mas and Guatemala and winters from the southern U.S. southward.
The black-tailed gnatcatcher lives in the deserts of the southwestern U.S.; the other species are found in Cen¬ tral and South America and Cuba.