The stereochemical nature of these oxygen glycosidic links is important in the
control of the metabolism of polysaccharides. Enzymes that catalyse the aque-
ous hydrolysis of the glycosidic links of polysaccharides will only usually cata-
lyse the cleavage of a link formed by a particular anomer or anomers. For
example, ana-glucosidase catalyses the hydrolysis of glycosidic links formed by
ana-glucose residue acting as a glycone in the polysaccharide chain.
1.4.5 The nomenclature of polysaccharides
Trivial names are normally used for all types of polysaccharide. Systematic
names may be used for small polysaccharides. These names are based on the
systematic names of the monosaccharides corresponding to the residues. How-
ever, the suffix-osylis used for a substituent residue joined through its anomeric
carbon to the next residue in the chain and the suffix-osideis used for the last
residue in the chain (Figure 1.19). Appropriate locants may or may not be used
in systematic names.
1.4.6 Naturally occurring polysaccharides
Naturally occurring polysaccharides can occur either as individual carbohy-
drate molecules or in combination with other naturally occurring substances,
such as proteins (glycoproteins) and lipids (glycolipids). In all cases the poly-
saccharide section may have linear or branched chain structures, which often
contain the derivatives of both monosaccharides and aminosugars (Figure 1.20).
HO OHHO OHHOH
HHHCOOHCOHO
OCH 3 CHCOOHOHHOHHHCH 2 OHNHCH 3HHOOHO
HHHCH 2 OHNH
COOHCH 3HHN-Acetyl-β-D-glucosamine (NAG) β-N-Acetylmuramic acid (NAM) β-D-Glucuronic acid
Figure 1.20 Some derivatives of monosaccharides and amino sugars commonly found in poly-
saccharidesPolysaccharides and molecules whose structures contain polysaccharide resi-
dues have a wide variety of biochemical roles. They occur as integral parts of the
structures of specific tissues: the mureins, for example, (Figure 1.21(a)) are
18 BIOLOGICAL MOLECULES