272 alsberg: biochemical analysis of nutrition 



groups are present one is in the alpha position ; the other is associ- 

 ated with the terminal carbon atom at the other end of the chain, 

 the omega position. Lysine is such a diamino-acid, as you can 

 observe from the .formula CH 2 (NH 2 )(CH 2 ) 3 . CH(NH 2 )COOH. 

 In these acids the atoms are arranged in a chain. However, 

 the protein molecule may contain amino-acids in which the 

 arrangement is such that a ring is found. Tyrosine, a benzol 

 derivative, is a good example. 



H NH 2 O 



I I II 

 C C— C — C— OH 



/% I I 



H— C C— H H H 



II I 



H— C C— H 



\s 



c 

 I 



OH 

 Histidine is another ring compound: 



H H 



I I 



II >CH 



I 

 H— C— H 



I 

 H— C— NH 2 



I 

 HO— C=0 



Tryptophane, which is related to indigo, is still another. The 

 proteins are combinations of a number of these amino-acids 

 with one another. Most of the seventeen or eighteen amino-acids 

 are found in each protein. In all probability each molecule of 

 protein contains a number of hiolecules of a given amino-acid, 

 so that the protein molecule may be very large. The union 

 of the amino-acids with one another is, so far as now known, 

 always of the same kind; the amino group of one acid is united 



