79 



(The amino acids in the Murchison meteorite are optically inactive, 

 unlike those in proteins, showing that both handed forms of a given 

 amino acid were present in roughly equal proportions; see fig. V-2.) 

 In addition to these fundamental building blocks of life, other 

 important classes of organic molecules have been identified. These 

 include heterocyclic bases, hydrocarbons, fatty acids, hydroxyacids, 

 etc. These solvent-soluble materials represent at most 30% of the 

 carbon found in these meteorites (or about 0.5% of the total meteor- 

 ite weight). The remaining carbon is predominantly present as a 

 solvent-insoluble phase. 



At this point it is important to remark that while the types of 

 organic compounds found in meteorites are consistent with those 

 expected to have served as precursors for the biochemicals of terres- 

 trial life, we do not know the details of their synthesis on the 

 meteorites. We cannot be sure that either the environments in which 



MIRROR 



H 2 N 



H 



C 



C COOH 

 H 3 



€ 



H 



C 



HOOC C NH 

 H 3 



o 



D -ALANINE 



L - ALANINE 



Figure V-2.- An important property of carbon is one that allows the formation 

 of two forms with identical composition - one form is the mirror image of the 

 other, just as the left hand is the mirror image of the right hand. Thus there are 

 two forms of alanine, L (levo-) the left handed and D (dextro-) the right handed 

 versions. The L-amino acids predominate in terrestrial biology. 



