O Hydrogen 



and specialized function which face us. High adventures in enzymology lie 

 ahead and many of the explorers will come from the training fields of carbo- 

 hydrate, fat, amino acid and nucleic acid enzymology. 



I feel now, as we did then, that for an effective approach to the problem 

 of nucleic acid biosynthesis it was essential to understand the biosynthesis 

 of the simple nucleotides and the coenzymes and to have these concepts and 

 methodology well in hand. It was from these studies that we developed the 

 conviction that an activated nucleoside 5 '-phosphate is the basic biosynthetic 

 building block of the nucleic acids (8). You will recall that the main pathways 

 of purine and pyrimidine biosynthesis all lead to the nucleoside 5 '-phosphate 

 (8); they do not, except as salvage mechanisms, usually include the free bases 

 or nucleosides. While the 2' and 3' isomers of the nucleotides are known, 

 they probably arise mainly from certain types of enzymatic degradation of 

 the nucleic acids. You will also recall from the biosynthesis of coenzymes (9), 



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