ON THE ORIGIN OF LIFE 



of compounds is to use heat with very little water. Fox and 

 co-workers (1957, 1958) have demonstrated the formation of 

 many peptide chains by heating either single amino acids or 

 mixtures, and suggest that similar processes may have been 

 important in early protein synthesis. In contemporary orga- 

 nisms, energy-requiring syntheses are driven by coupled reactions 

 in which energy-rich compounds such as adenosine triphosphate 

 (ATP) are broken down to yield the required energy. Although 

 it has been suggested that ATP was formed and accumulated in 

 the primeval sea (Blum, 1951), such a suggestion does not appear 

 plausible. Actually all the nucleotide triphosphates are ex- 

 tremely unstable when considered in terms of geological time. 



The most important biochemical problem at present in any 

 consideration of the origin of life is the synthesis of sufficient 

 amounts of the purine and pyrimidine nucleotides, the building 

 blocks of ribonucleic acid (RNA) and deoxyribonucleic acid 

 (DNA). The first difficulty is that no "natural" mechanism for 

 their synthesis has been proposed or demonstrated. In our repe- 

 tition of Miller's classic experiment, for example, we found no 

 evidence from ultraviolet-absorption measurements of material 

 having the high 2600 a absorption characteristic of nucleotides 

 and of purine and pyrimidine bases. The fact that compounds 

 of equal complexity, such as heme, can be made in the cell 

 from glycine and acetate (as stressed by Gaftron, 1960) is not 

 sufficient to demonstrate a "natural" mechanism, since those 

 reactions still require participation of enzymes. 



Not only do we lack evidence for an extra-vital synthetic 

 system, but we also lack sufficient information concerning the 

 stability of simple nucleotides. The purine deoxyribonucleo- 

 tides, for example, can exist for only a few hours in acid solu- 

 tion at room temperature. If it should turn out that many 

 nucleotides are not stable for long geological periods, we may 

 need to revise considerably our concepts concerning the com- 

 position of the first cells. Since it is extremely difficult to con- 

 ceive of a cell, however primitive, without nucleic aeid, studies 

 aimed at determining whether or not nucleic acid precursors 

 could have accumulated are urgently needed. Such studies 

 should include determination of the rate of breakdown of 

 nucleotides as a function of time, temperature, pH, and ionic 



