MACRO MOLECULES 



87 



Sometimes, the micelles may be randomly oriented as, for example, in 

 cellophane (Fig. 3). 



Fig. 3 (Mark) — Orientation of cellulose micelles in cellophane. 



(b) Starch — The most abundant reserve of carbohydrate in plants and in 

 microorganisms is starch, which on hydrolysis is transformed quantita- 

 tively into D-glucose. In the starch molecule the glucose molecules are 

 associated by l:4-a-glucoside linkages. From most starches two constitu- 

 ents may be isolated : 



(1) a straight-chain polysaccharide called amy lose which is coloured 

 blue by iodine. It consists of straight chains of variable length in which the 

 glucose units are linked by l:4-linkages and the number of units in each 

 chain varies from 100 to 2000. 



Fig. 4 (Miller) — Different t>'pes of starch granule. A, from the haricot bean ; B, from maize ; 

 C and Ci, from potatoes (c, simple granule; Ci, composite granule); d and D^, rice grains 

 (d, whole of the composite grain; Dj, one of the constituents of the grain at a higher 

 magnification); E, wheat grain; F, composite grain from oats. Note that each elementary 

 granule (a, b, c, Ci, Dj, e) has a number of concentric striations around an initial point, 



the hilum. 



