12 Can Science Explain Life? 



amino acids or their anhydrides (diketopiper- 

 azines), which may be represented generally as 

 follows : 



CO— OH CO— NH 



/ / \ 



-CH or — CH CH- 



\ \ / 



NH 2 NH— CO 



About thirty of these amino acids or their anhy- 

 drides have been isolated, the structural formulas 

 of the more important ones being as follows : 



