Chapter 7 SAQ 7.1 Identify each of the following statements as true or false If false give a reason for your response 1)D-xylose is a sugar commonly found in microbial polysaccharides 2) Pyruvate ketals contribute to the cationic nature of exopolysaccharides 3)The presence of acetate in exopolysaccharides increases their lipophilicity 4) Exopolysaccharides are not produced by yeasts and filamentous fungi 5)An exopolysaccharide containing a high content of D-ght ic acid will tend to bind cations 7.3 Exopolysaccharide structure As with all polysaccharides, microbial exopolysaccharides can be divided into homopolysaccharide and heteropolysaccha Homopolysaccharides contain only one type of monosaccharide, whereas heteropolysaccharides contain more than one Many are neutral glucans, being composed of the monosaccharide component D-glucose. 7.3.1 Homopolysaccharide types of homopolysaccharide are known(Figure e polyanionic homopolymers and, unlike the glucans, also contain acyl groups 1)Single linkage type. Several of these are neutral glucans, eg curdlan. Others Side chain type. Scleroglycan is typical and possesses tetrasaccharide repeating units due to a 1, 6p-D-glucosyl side-chain on every third main chain residue 3) Branched types. These are dextrans which are composed entirely of a-linked glucosyl residues. In some dextrans the linkage is almost entirely 1-6, but up to 50% of the glucose residues may be linked1→2,1→3or1→4198 Chapter 7 Identify each of the following statements as true or false. If false give a reason for your response. 1) D-xylose is a sugar commonly found in microbial polysaccharides. 2) Pyruvate ketals contribute to the cationic nature of exopolysaccharides. 3) The presence of acetate in exopolysaccharides inmases their lipophilicity. 4) Exopolysaccharides are not produced by yeasts and filamentous fungi. 5) An exopolysaccharide containing a high content of D-glucuronic acid will tend to bind cations. 7.3 Exopolysaccharide structure As with all polysaccharides, microbial exopolysaccharides can be divided into homoplysaccharides and heteropolysaccharides. Homopolysaccharides contain only one type of monosaccharide, whereas heteropolysaccharides contain more than one. Many are neutral glucans, being composed of the monosaccharide component D-glucose. 7.3.1 Homopolysaccharides Three main types of homopolysaccharides are known (Figure 7.2). 1) Single linkage type. Several of these are neutral glucans, eg curdlan. Others are polyanionic homopolymers and, unlike the glucans, also contain acyl groups. 2) Side chain type. Weroglycan is typical and possesses tetrasaccharide repeatingunits due to a 1,6-~-Dglucosyl side-chain on every third main chain residue. 3) Branched types. These are dextrans which are composed entirely of a-linked glucosyl residues. In some dextrans the linkage is almost entirely 1 + 6, but up to 50% of the glucose residues may be linked 1 4 2,1+ 3 or 1 + 4