PROXIMATE CONSTITUENTS OF THE ANIMAL BODY 53 



corresponding to the series of paraffins, and known as the fatty acids. Examples 

 of this group are : 



Formic acid Acetic acid Propionic acid Butyric acid 

 HCOOH CH 3 CH 3 CH 3 



COOH CH 2 CH 2 



I 

 OOOH CH 2 



I ' 

 COOH. 



In addition to these fatty acids, there are also unsaturated acids, derived 

 from the unsaturated hydrocarbons. 



DERIVATIVES OF THE FATTY ACIDS 



AMINO-ACIDS are derived from the fatty acids by the replacement of one 

 atom of hydrogen by the group NH 2 . 



Thus from propionic acid we may have : 



CH 2 .NH 2 CH 3 



I 

 CH 2 or CH.NH 2 



I I 



COOH COOH. 



The second form, the o-amino acid, is the only one which occurs in the body. 



OXYACIDS are formed by the replacement of one H atom by the group 

 OH. Thus: 



CH 3 



I 

 CHOH is oxypropionic acid or lactic acid. 



I 

 OOOH 



KETO-ACIDS. Oxyacids are formed by the oxidation of the group CH 2 

 or CH 3 . If at the same time the H 2 group be removed by oxidation a keto- 

 acid may be formed. This is probably the manner in which such acids arise 

 in the body, though it is more usual to regard a keto-acid as the result of oxida- 

 tion of a ketone. Thus : 



CO CO CO 



I ! I 



CH 3 CH 2 .OH COOH 



(acetone) (pyruvic acid 



a keto-acid) 



ACID AMIDES are formed from a fatty acid by replacing the -OH of 

 the -COOH group by -NH 2 , e.g. : 



CH 3 . CH 8 



from 

 CO.NH 2 COOH, 



(acetamide) (acetic acid) 



