82 



THE CHEMICAL COMPOSITION OF THE BODY 



H 



C H NH 2 



/\ I 



HC C C - C - C - COOH 



I I I 

 HC C CH H H 



C NH 

 H 



Tryptophane. 

 (Indol amino proprionic acid.) 



CH 3 NH. 



H-C-C-COOH 



I I 

 CH 3 H 



Valine. 

 (a-amino isovalerianic acid.) 



NH, 



NH. 



CH 3 H NH 2 



H-C-C-C- COOH 

 CH 3 H H 



Leucine. 

 (a-amino isobutylacetic acid.) 



H NH 



H-C-COOH 

 H-C-COOH 

 H 



=C-C-C-COOH 



I I I 



HN N H H 



C 

 H 



Histidine. 

 (a-amino /?-imidazol proprionic acid.) 



H-C-COOH 

 H-C-H 

 H-C-COOH 

 H 



A spar tic acid. Glutaminic acid. 



(amino succinic acid.) (a-amino normal glutaric 



acid). 



H H H NH 2 



I I 



H-N-C-C-C-C-COOH 



I I I 



NH=C H H H H 



I 

 NH 2 



Arginine. 

 (guanidine a-amino valerianic acid.) 



NH 2 H H H NH 2 



I I 

 H-C-C-C-C-C- COOH 



I I 

 H H H H H 



Lysine. 

 (a-e-diamino caproic acid.) 



The amino acids belong either to what is known in organic chemistry as 

 the aliphatic, carbocyclic, or heterocyclic series; that is, they are derivations 

 either of the hydrocarbons, of benzene or of closed-ring compounds not 

 composed wholly of carbon atoms, but in which one or more of the links 

 in the closed chain are supplied by other polyvalent elements (in the proteins 

 by nitrogen). Thus tyrosine and phenylalanine are carbocyclic compounds; 

 histidine, proline, and tryptophane are heterocyclic compounds, and the 

 remaining members of the list are aliphatic derivatives. 



Of the elements of the protein molecule, nitrogen is by far the most im- 



