Heteropolysaccharides branched

Pectin and pectic acid, which are the natural substrates of pectic enzymes, are branched heteropolysaccharides in which the backbone contains L-rhamnose residues and a-D-(l — 4)-linked residues of D-galactopyranosiduronic acid. The neutral sugars D-galactose and L-arabinose, and sometimes D-xylose and L-fucose, form the side... 

FIGURE 7-13 Homo- and heteropolysaccharides. Polysaccharides may be composed of one, two, or several different monosaccharides, in straight or branched chains of varying length. 

Hemicelluloses are constituted of different hexoses and pentoses glucose, mannose, xylose, etc. Since these heteropolysaccharides are often branched polymers, they cannot constitute crystalline structures. However, their function in the constitution of natural fibres is crucial. Together with lignin, they constitute the bonding matrix of the cellulose microfibres. 

Occurrence. D-Xylose (10) is present in widely abundant polysaccharides of plant tissues. Xylan is the main carbohydrate found in the hemicellulosic fraction, and accounts for one third of all renewable organic carbon available on earth. The structure and composition of xylans are variable, from linear (3-(l->4)-linked xylose chains to highly branched heteropolysaccharides. The branches may involve short oligosaccharides, usually of L-arabinofuranosyl units. Xyloglucans are also important hemicellulose polysaccharides consisting of a backbone of ( I — 4)-(i-D-glucopyranosyl residues heavily substituted with a-D-Xylp. Other monosaccharides may also be present.44... 

Polysaccharides are long polymers of monosaccharides and their derivatives. Unhke proteins or nucleic acids, these polymers can be either linear or branched, and they can contain only one type of monosaccharide (homopolysaccharides), or more than one (heteropolysaccharides). Polysaccharides can also be roughly divided into groups according to their two main functions energy storage and their contributions to structural components of cells. 

Polysaccharides are polymers of monosaccharide units. The monomeric units of a polysaccharide are usually all the same (called homopolysaccharides), though there are exceptions (called heteropolysaccharides). In some cases, the monomeric units are modified monosaccharides. Polysaccharides differ in the composition of the monomeric unit, the linkages between them, and the ways in which branches from the chains occur. Common polymers, their monomeric units, and linkages/ branches are shown below ... 

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