0-1,4-Glycosidic linkage cellulose chains

The small change in stereochemistry between cellulose and amylose creates a large difference in their overall shape and in their properties. Some of this difference can be seen in the strorcture of a short portion of fflnylose in Figure 25.9. The presence of the a-glycosidic linkages imparts a twist to the fflnylose chain. Where the main chain is roughly linear- in cellulose, it is helical in anylose. Attractive forces between chains are weaker in fflnylose, and fflnylose does not form the same kind of strong fibers that cellulose does. 

The parallels among chitin, cellulose, and HA structures, all being j3 -chains of hexose polymers are reflected in the striking similarity in sequence between the HAS from vertebrates, cellulose synthases from plants, and chitin synthases from fungi. A primordial ancestral gene must have existed from which all of these enzymes evolved that are involved in the biosynthesis of all polymers that contain -glycoside linkages, an ancient j3-polysaccharide synthase. 

Figure 9.25 Chemical structure of the polysaccharide cellulose, composed of long linear chains of glucose units connected as l -fi-glycoside linkages.

We have seen that the glycoside linkages of cellulose are broken by the action of acid, each cellulose molecule yielding many molecules of D-(H-)-glucose. Now let us look briefly at reactions of cellulose in which the chain remains essentially intact. Each glucose unit in cellulose contains three free —OH groups these are the positions at which reaction occurs. 

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