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Polysaccharides are considered to be polymers of monosaccharides containing ten or more monosaccharide residues. [2] Polysaccharides have been given trivial names that reflect their origin. [2] Two common examples are cellulose, a main component of the cell wall in plants, and starch, a name derived from the Anglo-Saxon stercan, meaning to ...
The formation of a glycosidic linkage results in the formation of a new stereogenic centre and therefore a mixture of products may be expected to result. The linkage formed may either be axial or equatorial (α or β with respect to glucose). To better understand this, the mechanism of a glycosylation reaction must be considered.
Polysaccharides, meanwhile, have a general formula of C x (H 2 O) y where x and y are usually large numbers between 200 and 2500. When the repeating units in the polymer backbone are six-carbon monosaccharides , as is often the case, the general formula simplifies to (C 6 H 10 O 5 ) n , where typically 40 ≤ n ≤ 3000 .
Specifically, it is the phosphodiester bonds that link the 3' carbon atom of one sugar molecule and the 5' carbon atom of another (hence the name 3', 5' phosphodiester linkage used with reference to this kind of bond in DNA and RNA chains). [3] The involved saccharide groups are deoxyribose in DNA and ribose in RNA.
The terms glycans and polysaccharides are defined by IUPAC as synonyms meaning "compounds consisting of a large number of monosaccharides linked glycosidically". [1] However, in practice the term glycan may also be used to refer to the carbohydrate portion of a glycoconjugate, such as a glycoprotein, glycolipid, or a proteoglycan, even if the carbohydrate is only an oligosaccharide. [2]
Amylose A is a parallel double-helix of linear chains of glucose. Amylose is made up of α(1→4) bound glucose molecules. The carbon atoms on glucose are numbered, starting at the aldehyde (C=O) carbon, so, in amylose, the 1-carbon on one glucose molecule is linked to the 4-carbon on the next glucose molecule (α(1→4) bonds). [3]
Chitin is a modified polysaccharide that contains nitrogen; it is synthesized from units of N-acetyl-D-glucosamine (to be precise, 2-(acetylamino)-2-deoxy-D-glucose). These units form covalent β-(1→4)-linkages (like the linkages between glucose units forming cellulose).
Levan in the branched from with beta 2,1 glycosidic linkages. Levan is a naturally occurring fructan present in many plants and microorganisms. [1] This polymer is made up of fructose, a monosaccharide sugar, connected by 2,6 beta glycosidic linkages. Levan can have both branched and linear structures of relatively low molecular weight. [2]