Glycoconjugates and Carbohydrates

Glycosaminoglycan Polysaccharide chain found in proteoglycans. Has a linear structure that features a repeating disaccharide unit comprised of glucosamine or galactosamine and a uronic acid or galactose. The amino sugars are generally N-acetylated and contain ester sulfate. The pattern of sulfation varies and may confer specific biological properties. Glycoside Acetal or ketal formed by substitution of the anomeric hydroxyl with an aglycone. This reaction fixes the configuration at the anomeric center. Linkages are generally acid labile. Ketose (ulose) Polyhydroxy ketone (at carbon 2) of four or more carbon atoms (see Aldose). Mutarotation The change in optical rotation associated with the equilibration, in solution, of the anomeric and ring forms of a saccharide beginning with a single crystalline form. Thus, dissolving a-D-glucopyranose in water allows formation of the j-anomer as well as the furanose forms. Since all have different optical rotations, the initial value changes until the equilibrium mixture is achieved. Oligosaccharide Sugars that contain 2-10 monosaccha-ride units. These may be linear or branched. The most common representatives are derived from aldoses and will contain a single reducing terminus (free, or potential, aldehydo group) and one or more nonreducing termini (linked to other sugars only at their anomeric hydroxyl group). Polysaccharide Structure containing more than 10 monosaccharide units. These may be the same (homo-polysaccharide) or different (heteropolysaccharide), and the structure may be linear or branched. Natural diversity is very large. Proteoglycan Special category of glycoproteins in which the saccharide chain is covalently linked to protein via an initiating xylose residue, a specific core oligosac-charide, and is followed by a glycosaminoglycan chain.

Pyranose Six-membered ring form of a saccharide formed by reaction of the appropriate hydroxyl group with the carbonyl carbon. Generally the most stable structure in solution. The conformer resembles cyclo-hexane and is generally a chair form with axial and equatorial substituents.

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