Gene Action and Polypeptides 



411 



depend upon what each of these two genetic 

 areas does individually, it is considered that 

 two genes are involved, and that each gene 

 completely specifies a polypeptide chain. 



The union of the two chains comprising 

 tryptophan synthetase may somehow be re- 

 lated to the two genes involved being adja- 

 cent. 



figure 32-4. The twenty types of common amino acids. 



THREONINE (THR) ASPARTIC ACID (ASP) ASPARAGINE (ASN) GLUTAMIC ACID (GLU) GLUTAMINE (GLN) 



CYSTEINE (CYS) 



H H O 



I I II 



H — N — C— C — O— H 



I 



H — C — H 



I 



S — H 



METHIONINE (MET) 



H H O 



I I II 

 H— N— C — C— O— H 

 I 



H — C— H 



H- 



H — C- 



I 

 H 



-H 



TYROSINE (TYR) 



H H O 



I I II 

 H — N — C— C— O— H 



TRYPTOPHAN (TRY) PHENYLALANINE (PHE) 



H H O H H O 



I I II I I II 



H — N — C — C— O— H H— N— C— C— O— H 



I I 



H — C — H H— C— H 



I X H I 



c=c 



X 



N — H 



