Genes: Nature and Mode of Action - 523 



DNA 

 DOUBLE STRAND 



SEPARATED 

 SINGLE STRANDS 



TEMPLATED 



PICK-UP OF 



COMPLEMENTARY 



BASES 



SELF-TEMPLATED 

 REPLICATION 

 COMPLETED. 

 TWO DOUBLE- 

 STRANDED 

 UNITS 



Fig. 27-3. Crick hypothesis on fhe mechanism of DNA replicafion. Note that 

 the base-pair rule operates in the assembling of the nucliotides. As a result 

 of such self-templated replication, each of the new DNA units is an exact copy 

 of the original. Symbols in the sugar-phosphate chain are S and P, respectively; 

 in the base pairs, A, T, G, and C are adenine, thymine, guanine, and cytosine, 

 respectively. 



along each of the separate single strands. 

 Finally a new sugar-phosphate chain is 

 formed, and a re-coiling of the double helix 

 occurs. In short, each single strand serves as 

 a template for the building of a complemen- 

 tary strand; and finally, each of the new 

 double helices constitutes an exact replica of 

 the original one. A complex sort of auto- 

 catalysis has occurred. 

 Recent evidence strongly supports this con- 



cept of the mechanism of DNA replication. 

 Particularly important in this regard are the 

 experiments of Arthur Kornberg at Wash- 

 ington University. Kornberg worked on the 

 synthesis of DNA in cell-free bacterial prepa- 

 rations (see below). Also important are the 

 studies on viral DNA replication conducted 

 by T. F. Anderson and S. S. Cohen at the 

 University of Pennsylvania, A. D. Hershey 

 and M. W. Chase at the Carnegie Laboratory 



