604 



METABOLISM 



Two cysteine molecules united at the "S" groups give cystine. 



NIL 1 



/ 



I 1 1 .,& — CII 



\ 



coon 



NH, 



3. Phenylalanine has a C 6 R i (phenyl) group, CH,C 6 H 5 -CH 



/ 



\ 



4. Tyrosine has a C 6 H 4 OH (phenol) group, CH,C 6 H 4 OH - CH 



COOH 



NH., 

 / 



\ 



COOH 

 C 



/ \ 



5. Tryptophane has a C 6 H 4 CH (indole) group: 



\ / 

 NH 



C — CH, - CH - NH, - COOH. 



/ \ 

 C B H 4 CH 



\ / 

 NH 



CH 



/ \ 

 N NH 



I ! 



6. Histidine has a CH = C - (imidazole) group: 



CH 



/ \ 

 N NH 



I ! 



CH = C.CH_, . CH. NH,-COOH. 



The last two are also called heterocyclic compounds, of which there 

 is another, viz.; 



Proline (and oxyproline), which is a-pyrrolidine carboxylic acid: 



CH, — CH, 



Other amino acids are 



(1) Valine 

 Leucine 

 Isoleucinc 

 thus: 



