50 



CARBOHYDRATES 



made up of many molecules of one or more simple sugars combined 

 by glycosidic linkages. For example, a molecule of the polysaccharide 

 amylose, a form of starch, consists of about 200-300 glucose units 

 attached to each other by a-l,4-linkages as shown by the following 

 formula: 



CH2OH 



CH,OH 



CH.OH 



H 



OH 



CH2OH 



jAo^V_i 



H 



Amylose 



Only four glucose units are shown in this formula, the rest merely being 

 indicated to save space by the n outside the brackets. This abbreviation 

 means that the part inside the brackets is repeated n times in the com- 

 plete formula, n being about 100-150 maltose units in this particular 

 ease. Thus amylose, like all polysaccharides, is a very large molecule, 

 far bigger than the mono-, di-, and trisaccharides so far considered. 

 The molecular weight of amylose is in the range of 10,000-100,000 (no 

 exact value can be determined), whereas sucrose, for example, has a 

 molecular weight of only 342. Polysaccharides in general have molecular 

 weights ranging from a few thousands to several millions. 



The example given above, amylose, represents the simplest type of 

 polysaccharide structure, i.e., a long series of simple sugar residues, all 

 of the same kind attached to each other in a single long chain. A second 

 type consists of a branching structure rather than a single chain. Gly- 

 cogen is an example of this type of polysaccharide. Its structure is 

 indicated by the following diagram, in which each small circle repre- 

 sents a glucose unit: 



o 

 o 



o 000 O OOOo 



% 



o 

 o 



o 



0° 



o o 



o o 



o o 



o o 



o 

 o 



o 



o 



o 



o 



o 



00000000000000000000 



ooooooo 0000000000 



o o 



o o 



o o 



0000000000000 00 00 00 000 o o 



o 2 



o nOO°°° ooo 



OOO ^0° O .aO° 



0^0 



o 

 o 

 o 

 o 

 o 



o"Oo o^ 



•oo 



000 



Diagram of glycogen, a branched polysaccharide 



