86 



As an example, the decarboxylation of the nucleotide of orotic 

 acid is one of the steps in the biosynthesis of the nucleotides of 

 uracil and cytosine. This same decarboxylation is a key reaction in 

 the prebiotic synthesis of uracil from HCN. In addition, aspartic acid, 

 the starting material for the biosynthesis of orotic acid, is produced 

 in a variety of prebiotic experiments. It would not have been a major 

 change for early life to evolve a system for the biosynthesis of orotic 

 acid from the readily available aspartic acid once the low supply of 

 preformed orotic acid limited the growth of primitive life forms. 



INORGANIC ASPECTS 



While much of the work in the study of chemical evolution and 

 the origins of life have dealt with the formation, polymerization, 

 and interaction of important organic molecules, there is an awareness 

 on the part of most students of the field that inorganic chemistry 

 was undoubtedly of fundamental importance in the processes respon- 

 sible for the origins of life on Earth. Since it is known that all life on 

 Earth now requires the metal ions for its chemical function, a num- 

 ber of scientists have questioned at what stage such fundamental 

 processes became important. Early in the history of this field of 

 study, Granick suggested that the first organization of preprotoplasm 

 could be a primitive energy-conversion unit that could perform the 

 elementary processes of photosynthesis and respiration; that this 

 unit originated within the domain of some common minerals; that 

 the minerals that contain metal ions served both as coordinating tem- 

 plates and catalysts for various reactions; and that around this unit 

 were formed organic molecules that gradually became organized into 

 units of ever-increasing complexity. Thus, biosynthetic chains devel- 

 oped in a stepwise fashion. The metal catalysts of minerals became 

 modified into the metalloenzymes; in these new complexes the same 

 metals would become more efficient. 



In a similar vein, Bernal had earlier suggested in his book "The 

 Physical Basis of Life" that clays were sites upon which organic 

 molecules could be concentrated and react with each other. 



In recent years, studies of the role of metal ions and minerals in 

 prebiological chemistry have shown promising results. As noted 



