The Origin of Life 9 



taneous protein-generation reaction lies on the side of dissolution 

 rather than synthesis. Wald suggests, nevertheless, that molecules 

 seem to be able to resist dissolution both through large size and 

 through aggregation with other molecules. Proteins may be an un- 

 stable mid-point, subject either to dissolution into their component 

 amino acids or to the formation of more stable aggregates. The first 

 "organisms" may well have been the result of the formation of larger 

 and larger aggregates. 



ENERGY SOURCES 



Ultraviolet light usually is considered the chief source of energy 

 for early synthetic processes. With simple molecules, only very 

 short wavelengths are absorbed, but as more complex molecules 

 appear, absorption of longer ultraviolet wavelengths takes place. As 

 the earth evolved its thick atmospheric layers, ultraviolet of short 

 wavelengths no longer could penetrate to the earth's surface to be 

 used as an energy source. The appearance of colored pigments 

 (e.g., porphyrins mentioned below) made possible the absorption 

 of energy in the visible spectrum. However, whatever the source of 

 energy, there is a considerable gap between the absorption of a 

 quantum of energy and its mobilization for use in biological proc- 

 esses. 



The problems of utilizing energy for protein synthesis and the 

 conditions under which it may occur are particularly vexing ones. 

 In present-day biological systems the enzymes responsible for the 

 mobilization of energy and for the synthesis itself are proteins. Thus 

 if one is to postulate the functioning of such systems in the forma- 

 tion of the first proteins, he becomes embroiled in a "chicken or egg" 

 dilemma. It has been suggested that, in the absence of proteins, 

 other substances (e.g., clays) may have served as catalysts, since 

 many of the known enzymatic phenomena are fundamentally mole- 

 cule-surface reactions. This raises the question of how proteins sub- 

 sequently came to assume this function. At least it can be said that 

 the surface phenomena of clays and surface configurations of pro- 

 teins have certain aspects in common. 



Chemical energy for synthesis in modern biological systems in- 

 volves organophosphate bonds that yield exceptionally high energies 

 upon cleavage. The energy released upon cleavage or transfer of 

 these bonds is regulated by a complex system of catalysts ( enzymes 

 plus their coenzymes); the characteristics of these sets of reactions 

 are unique to hving systems. They change velocity in response to 

 changes in concentration of product; are dependent upon physical 



