328 CHAPTER 35 



ment of the 3' phosphate to sugar linkages. at places in a polypeptide chain where lysine 



Finally, special attention should be drawn or arginine are present. The DNA synthe- 



to the polymerizing enzyme essential for the sizing enzyme, DNA polymerase, is unique 



extended biological synthesis of DNA. Previ- in that it takes directions from a template; 



ously known enzymes are specific in the in lengthening a strand it adds the particular 



respect that they act upon one or a few par- component of the substrate which is of the 



ticular substrates which are usually modified proper size and which will form the correct 



in the same way. Recall (p. 287), for ex- hydrogen bonds with the base on the single 



ample, that trypsin breaks peptide bonds only strand acting as template. 



SUMMARY AND CONCLUSIONS 



DNA can be synthesized in vitro. Extended synthesis requires pre-existing single-stranded 

 DNA, the 5' triphosphates of deoxyadenosine, of deoxycytidine, of deoxyguanosine, and 

 of thymidine, Mg ions, and a polymerizing enzyme. In making the product the polymerase 

 takes directions from pre-existing single-stranded DNA. 



Study of the physical and chemical properties of the synthesized product reveals that it 

 closely resembles natural DNA and possesses the primary and secondary structure of DNA 

 as elucidated by Watson and Crick. This DNA synthesis is considered to be a biological 

 process. 



These results may also be considered as offering further support for the Watson-Crick 

 structure of chromosomal DNA and for its replication after chain separation through the 

 formation of complementary strands. 



REFERENCES 



Trautner, T. A., Swartz, M. N., and Romberg, A., "Enzymatic Synthesis of Deoxyribo- 

 nucleic Acid, X. Influence of Bromouracil Substitutions on Replication," Proc. Nat. 

 Acad. Sci., U.S., 48:449-455, 1962. 



See Supplement VI. A list of references can be found at the end of Dr. Kornberg's Nobel 

 Prize lecture. 



QUESTIONS FOR DISCUSSION 



35.1. Has this Chapter dealt with genetics? Explain. 



35.2. Which single experiment described in this Chapter would you consider to be the most 

 important? Why? 



35.3. Differentiate between the action of splenic phosphodiesterase and snake venom di- 

 esterase. 



35.4. What are the requirements for the in vitro synthesis of DNA to proceed as a limited 

 reaction? To proceed extensively? 



35.5. What differences exist between DNA chain formation in vitro in the absence and 

 presence of primer DNA? 



35.6. List the evidences that the synthesis of DNA in vitro represents a biological process. 



35.7. Does DNA polymerase from E. coli take directions only from E. coli DNA? Explain. 



35.8. Does chain separation occur during an extended synthesis of DNA in vitro? Explain. 



35.9. Of what significance is the nearest nucleotide neighbor analysis? 



