glycoside

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Glycoside

A large important class of sugar derivatives in which the sugar is combined with a nonsugar. In their cyclic forms, monosaccharides (simple sugars) possess one carbon (C) atom (the anomeric carbon) that is bonded to two oxygen (O) atoms; one oxygen atom forms a part of the ring, whereas the other is outside the ring (exocyclic) and is part of a hydroxyl (OH) group. If the oxygen atom of the anomeric hydroxyl group becomes bonded to a carbon atom, other than that of a carbonyl (C ═ O) group, the resulting compound is a glycoside. A glycoside thus consists of two parts (see illustration): the sugar (glycosyl) unit, which provides the anomeric carbon, and the moiety (the aglycon), which is the source of the exocyclic oxygen and carbon atoms of the glycosidic linkage. Such compounds frequently are referred to as O-glycosides to distinguish them from analogs having a sulfur (thio- or S-glycosides), nitrogen (amino- or N-glycosides), or carbon (anomalously called C-glycosides) as the exocyclic atom on the anomeric carbon. See Monosaccharide

The formation of glycosides is the principal manner in which monosaccharides are incorporated into more complex molecules. For example, lactose (illus. b), the most abundant disaccharide in mammalian milk, has a glycosidic bond involving the anomeric carbon of d -galactose and the C-4 hydroxyl of d -glucose. The anomeric carbon atom can exist in either of two stereoisomeric configurations, a fact which is of immense importance to the chemistry and biochemistry of glycosides. For example, the principal structural difference between cellulose and amylose is that cellulose is β-glycosidically linked whereas amylose is α-linked. Humans are able to digest amylose but are unable to utilize cellulose for food. See Cellulose, Lactose

Structural formulas of two glycosidesenlarge picture
Structural formulas of two glycosides

A very large number of glycosides exist in nature, many of which possess important biological functions. In many of these biologically important compounds the carbohydrate portion is essential for cell recognition, the terminal sugar units being able to interact with specific receptor sites on the cell surface.

One class of naturally occurring glycosides is called the cardiac glycosides because they exhibit the ability to strengthen the contraction of heart muscles. These cardiotonic agents are found in both plants and animals and contain complex aglycons, which are responsible for most of the drug action; however, the glycoside may modify the biological activity. The best-known cardiac glycosides come from digitalis and include the drug digoxin.

Glycosidic units frequently are found in antibiotics. For example, the important drug erythromycin A possesses two glycosidically linked sugar units. See Antibiotic

Perhaps the most ubiquitous group of glycosides in nature is the glycoproteins; in many of them carbohydrates are linked to a protein by O-glycosidic bonds. These glycoproteins include many enzymes, hormones, such antiviral compounds as interleukin-2, and the so-called antifreeze glycoproteins found in the sera of fish from very cold marine environments. See Amino acids, Carbohydrate, Enzyme, Glycoprotein, Hormone

Glycolipids are a very large class of natural glycosides having a lipid aglycon. These complex glycosides are present in the cell membranes of microbes, plants, and animals. See Glycolipid, Lipid

glycoside

[′glī·kə‚sīd]
(biochemistry)
A compound that yields on hydrolysis a sugar (glucose, galactose) and an aglycon; many of the glycosides are therapeutically valuable.
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Dort yuz doksan alti mesane tumorlu hastanin idrar orneklerinin incelendigi calismada erken evredeki tumorlerde bile bu iki genin siklikla metile oldugu gorulmustur.
Bu calisma, gerek analize alinan kromozom bolgeleri acisindan, gerekse kritik rekombinasyonlarin tam olarak gozlenebildigi uc kusaga uygulanabilirligi acisindan sasilik alaninda bir ilki gerceklestirmektedir ve ozgul genin belirlenmesine yonelik gelecek calismalar icin isik tutacaktir.
Ayrica bu tur arastirmalarda, sadece islevsel acidan onemli oldugu bilinen bolgeler yerine, genin tamaminin taranmasi yeni ve orijinal sonuclara ulasmak konusunda daha yararli bir yaklasim gibi gorunmektedir.
2], calculada por Genin y Alzerreca (2006) para estepas arbustivas.
Kemik mineral yogunlugunu (KMY) etkileyen bir cok cevresel faktor olmasina ragmen son yillarda yapilan calismalarda genetik yapinin osteoporoz patogenezindeki etkisi uzerinde durulmus ve kemik kutlesi uzerine etkisi olan bir cok aday genin varligi rapor edilmistir.
Genin expressed during his speech his deep feelings and happiness to be in the town of Beit Sahour that has had a strong twinning agreement with his city for many years, reiterating that this agreement would continue in the future.
Bu genin urunu, bakir transporte eden zar proteinidir ve disfonksiyonu barsak hucrelerinden kan dolasimina bakir gecisini onler.
Asi, de cara a una decision complicada, en la cual dos o mas logicas de naturaleza diferente se ven confrontadas (verbigracia la familia frente a la empresa), los dirigentes de firmas familiares pueden presentar comportamientos disfuncionales o irracionales (Cisneros & Genin, 2010).
Albitar S, Bourgeon B, Genin R, Fen-Chong M, N'Guyen P, Serveaux MO et al.