60 mavricp: .i. hkssman 



VII. Conclusions 



Tlio pathway of DNA synthesit; in E. coli and calf tliyinus studied 

 in vitro arc similar in several respects. We may considci- the formation 

 of deoxyribonucleotides as the initial reaction in the metabolic sequence 

 leadino; specifically to DNA. The reduction of lihonucleotides to the 

 corresponding deoxyrihosyl dcrixatives, the phosphorylation of these 

 derivatives and their sui)se(iuent polymerization into the macionioh'culc 

 are being studied as individual reactions in purified systems. 



The biological aspects of DNA synthesis, such as cellular growth 

 and pi'oliferation, genetic continuity, and metabolic control, are depend- 

 ent on the individual enzymatic steps in this pathway and are therefore 

 influenced by the physical i)roperties of the enzymes and tlie chemical 

 properties of the reactions. Lord Kelvin said, "When you can measure 

 that of which you speak, and express it in numbers, you know something 

 about it." The detailed biochemical investigations of the individual steps 

 in this sequence are providing the "numbers'" indispensable in arriving 

 at a satisfactory descrijition of the biological pi'ocess and are establish- 

 ing a foundation for the formulation of hyj^otheses necessary to this area 

 of research. 



ACKNOW^LEDG M EN TS 



I should like to thank Dr. Arthur Kornberg, Dr. John Josse, and Dr. Fnnl J. 

 Bollum for letting me use material which had not yet been published. 



Thanks are also due to Mrs. Mary E. Backer for expert assistance in tlu- 

 preparation of the manuscript, and to the people in my laboratory for li\ing with 

 mo (luring this period. 



This manuscript was written during the tenure of a grant (C-4088) from the 

 U. S. Pubhc Health Service. 



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