24 



UNITY AND DIVERSITY IN BIOCHEMISTRY 



(g) Oxidation Products of Sugars 

 {Monoacidic Polyalcohols, or Polyacids) 



Under controlled conditions oxidation of aldoses can give rise either to 

 aldonic acids resulting from oxidation of the aldehyde group to a carboxyl 

 group, or to uronic acids in which the aldehyde group is preserved and the 

 primary hydroxyl is oxidized to carboxyl, or finally to dicarboxylic acids 

 having a carboxyl at each end. In the case of glucose the following com- 

 pounds are obtained : 



CHO 



! 



(CHOH)4 

 CHoOH 



Glucose 

 (aldose) 



COOH 



(CHOH)4 

 CHoOH 



Gluconic acid 

 (hexonic acid) 



CHO 



(CHOH)4 

 COOH 



Glucuronic acid 

 (uronic acid) 



COOH 



(CHOH)4 

 COOH 



Saccharic acid 

 (dicarboxylic acid) 



Numerous hexonic, uronic and dicarboxylic acids derived from the 

 aldoses are present in nature. 



C. Amino Acids 



{a) Definition 



The amino acids are defined as substances having a carboxyl and an 

 amino group together in the same molecule. The number of substances 

 falling into this category which organic chemists can synthesize is very 

 great but only a limited number of these compounds are present in the 

 biosphere. The amino acids usually have the amino group in a position a to 

 the carboxyl group, so that their general formula is : 



NHa 



R— CH— COOH 



REFERENCES 



HoNEYMAN, J. (1948) An Introduction to the Chemistry of Carbohydrates. Clarendon 



Press, Oxford. 

 PiGMAN, W. W. & GoEPP, R. M. (1948) Chemistry of the Carbohydrates. Academic 



Press, New York. 



