CARBOHYDRATES, CHITIN AND CUTIN 



311 



consist of unbranched chains, whereas amylopectin is made up of 

 branched chains (Staudinger and Husemann, 1937; Staudinger, 

 1937 b) which together form a gel framework (Fig. 152); consequently 

 amyloses are soluble, which amylopectin is not. Their other properties 

 are given in Table XXVIII. In different starch samples the content of 



^P?P^$:R>R?Ri3^PR? 



b) c) 



Fig. 152. Diagram of the molecular shapes of starch molecules. Glucose residues repre- 

 sented as small rings: they are far more numerous (degree of polymerization) than shown 

 here, a) Expanded amylose chain (cf. cellulose), b) Amylopectin (from K. H. Meyer, 

 1943): branched chain molecule. At x signs of the activity of the sugar-forming amylase: 

 splitting off of the disaccharide maltose. In the absence of the dextrin-forming amylase, 

 ■degradation ceases if maltose has split off from all the free terminals up to the branching 

 place, c) Glycogen: highly branched starch molecule. 



TABLE XXVIII 

 COMPARISON BETWEEN AMYLOSES AND AMYLOPECTIN 



Amyloses 



Amylopectin 



Molecular configuration 



Molecular weight (osmot.) 



j3-Amylase 



Pasting 



Films 



Tetramethyl glucose 

 from maize starch 



Unbranched chain 

 1 000c - 1 00000 

 Complete hydrolysis 

 Forms no paste 

 Solid film 



0.51% 

 almost nil 



branches/molecule 



Branched molecule 

 5 0000 - 1 000000 

 Malto dextrin 

 Forms paste 

 Friable film 



3-7% 

 about 100 



branches/molecule 



amylose varies from 34% to 0% (Table XXIX). The blue starch 

 reaction with iodine is limited to amyloses with crystallized chains, 

 i.e., unbranched chains orientated in parallel (Meyer and Bernfeld, 

 1941a), or to individual amylose chains wound up into a helix. 



