88 



UNITY AND DIVERSITY IN BIOCHEMISTRY 



(2) a highly branched polysaccharide, amylopectin, which is coloured 

 violet by iodine. The smaller side-chains are attached to the main branches 

 by l:6-a-linkages (isomaltose). The side-chains themselves, like the main 

 chain, are built up of l:4-a-glucoside linkages. 



Certain starches contain only amylopectin. This is the case for the 

 starches from maize and rice. 



When a starch is made up of amylopectin and amylose, the proportion 

 of the latter, like the length of its chains, varies according to the source. 



CH.OH 



CHtOH 



CH.OH 



CH.OH 



Ot- 



)H H OH 



AMYLOSE 



CH2OH 



CHiOH 



...O- 



O H 



O---- 



Branching by 1 : 6-a-linkages in amylopectin 



(c) Glycogen — Glycogen, the major carbohydrate reserve in animals, is 

 a branched polysaccharide similar to amylopectin. It is made up of 

 D-glucose units. It is coloured brown by iodine and is water soluble 

 (15 to 20%). Glycogen is more highly branched than amylopectin and, 

 consequently, it contains a greater proportion of l:6-a-glucoside linkages. 



