376 CARBOHYDRATE METABOLISM 



organic solvents. One of the few liquids which will dissolve it is an am- 

 moniacal solution of copper hydroxide (Schweitzer's reagent). Concen- 

 trated sulfuric acid will gradually hydrolyze cellulose into glucose, while 

 dilute sulfuric acid causes it to swell and converts it into "hydrocellulose." 

 In sodium hydroxide solutions of about 15 per cent, cellulose swells, also 

 producing a "hydrocellulose"; this effect is the basis of the process of mer- 

 cerization. Stepwise hydrolysis of cellulose results first in the production of 

 cellobiose, a disaccharide, each molecule of which is in turn hydrolyzed into 

 two molecules of glucose. 



Next to cellulose, starch is undoubtedly the most abundant hexosan oc- 

 curring in plants. Starch "molecules" are built up by the linear condensation 

 of many molecules of a ^-glucose, each glucose residue being connected to 

 the next by an oxygen bridge. The difference between starch and cellulose 

 is shown in the following two structural formulas, one of which represents 

 three of the glucose residues in a starch molecule, the other three of the 

 glucose residues in a cellulose molecule. 



H OH H OH H OH 



i i A i () C 



--0-1/0H H\r-o^/oH h\^o-i/oh hV- 



n C C C C C 



A|_o/^ h\Lo/h H^I^ 



CH,OH CH.OH ^^^^^^ OT.OH 



H OH CH2OH H OH 



h i i o h — c 



c c c c c c 



i\h /^o-J\oh h/i i\h /•- 



I 111 



CH2OH H OH CH2OH 



Cellulose 



Starch is an almost universal form of storage carbohydrate, since there 

 are very few of the higher green plants in which this compound does not 

 accumulate in some organ of the plant. Of the relatively small group of 

 plants which do not form starch, the onion, leek, snowdrop, and dahlia are 

 some of the more familiar species. The failure of the plants in this group 

 to synthesize starch is sometimes ascribed to a lack of the proper enzymes, 

 although in some species it is apparently due to failure of a high enough 



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