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cause of van der Waals' forces. 



CHARGAFF: Another one, not dissimilar, can be described. Not 

 this particular one. Because of the pitch of the helices, it is not possible to 

 accomodate 2' hydroxyls. 



CARTER: The novel feature here is that it utilizes very nicely Dr. 

 Chargaff's data which showed that there is always a ratio of adenine and thymine 

 approaching 1, and similarly guanine and cytosine. 



This helical structure is held together by the phospho-di-ester linkage 

 and also by hydrogen bonding between purines and pyrimidines, adenine and 

 thymine, guanine and cytosine, hydrogen bonding that develops about the 1 and 

 6 positions in the purine and pyrimidine rings. The hydrogen bonding gives 

 orientation, specificity, and rigidity to this structure. The sequences develop 

 in opposite directions in the 2 chains. 



The double helical model provides a mechanism for replication or re- 

 duplication of the structure. 



It is an apparently satisfactory statement of structure, and a formula- 

 tion upon which experiments can be based. It is a phenomenon that is almost 

 unparalleled in modern scientific publication. Watson and Crick formulated 

 this structure and within a few months 8 or 10 people have rushed into the litera- 

 ture to prove that they are right. That does not happen very often. 



CHARGAFF: No, people rushed in 5 years before they published it to 

 prove they were right. Actually, Wilkins, Franklin and Gosling had excellent 

 X-ray data which were published. 



CARTER: It was their data that Watson and Crick used. 



CHARGAFF: I think you might say that Watson and Crick were con- 

 firmed 5 years before they published their hypothesis. 



POTTER: Could you comment on the Watson-Crick structure from 

 the standpoint of how the experiment fits biological specificity? 



CARTER: There is specific orientation. 



POTTER: It is all on the inside, isn't it? 



CARTER: The chain comes out of the helix and there is an opportunity 

 for replication on each strand. 



SPIEGELMAN: There is one piece of information which was given at 

 the National Academy meeting. The titration curves do not completely fit the 

 Watson-Crick model. There are too many free titratable phosphate groups. 

 And the suggestion was made by Dr. Schachman, that there are breaks along the 

 chain so that not every phosphate group is di-esterified along the chain. Stent 

 has done some ingenious experiments, which would really take too long to de- 

 scribe, in an attempt to see if the breaks are distributed at random along the 

 molecule. The data he had just before the Academy meeting were still prelimi- 

 nary, but they fit beautifully with the idea that the molecule is not continuous. 



CARTER: Yes, in their formulation they talk about chains having 2100 

 units or something higher than that. This business of end groups is extremely 



