40 Nature of the Genetic Material 



to see how these processes occur without evenihing getting tangled, 

 we do not feel that this objection will be insuperable." (I suggest 

 that the weakest hnk in the reasoning is the transition from molecule 

 to chromosome. We shall return to this important point.) 



According to Watson and Crick, the new structure of the DNA 

 molecule is an open one. Between the coupled chains, room is left 

 for pohpeptide chains to wind around the same hehcal axis. The 

 distance of 7.1 A between adjacent P-atoms is close to the repeat of 

 a fully extended pol\-peptide chain (Astbur\', 1939). "The function of 

 the protein might well be to control the coiling and uncoiling, to 

 assist in holding a single nucleotide chain in a helical configuration 

 or some other non-specific function." Thus the new theon.' clearly 

 attributes to the DNA the specific, that is, the genetic, function and 

 to the protein moiety a secondary, non-genetic one, that is, the op- 

 posite of what many geneticists assume. The protein now becomes the 

 first product of the genie DNA. This is the conclusion which must be 

 weighed against all the c\'tological and genetic evidence. 



So much work is in progress on this subject that almost ever\- 

 month new facts and ideas come to light. Gamow (1954) has begun 

 to develop a mathematical theory- of how amino acids are assembled 

 at the surface of the bases in a definite order. Dekker and Schach- 

 mann ( 1954 ) propose that the tsvo hehcal strands are composed of 

 fairly large molecules with alternate interruptions which permit the 

 formation of a long chain. Much interest is concentrated also upon 

 the derivation of RNA from DNA; the importance of this problem 

 \%ill become apparent in a subsequent chapter. 



These are certainly far-reaching and exciting facts, and it will be 

 important to see whether further biochemical work wHl confirm the 

 correctness of the basic assumptions. The geneticist, who is anxiously 

 waiting for the biochemist to explain some of his diflBculties, will 

 grasp these new ideas, though he is rarely prepared to weigh the 

 biochemical evidence. However, he will not be content to accept a 

 fine explanation of self-dupHcation as proof that the substance in 

 question, DNA, is the genie material. Such a proof requires agree- 

 ment with the entire body of biochemical, genetical, and cvtological 

 facts discussed in this chapter, and the exclusion of alternative inter- 

 pretations. 



It is at once clear that there should be no difficult^' in re\ersing 

 the theon.- and concluding that the DNA molecule is the scaffold 

 which keeps the proteinic genie material in place for its reduphcation, 

 which might be coincident or not with the DNA duphcation as de- 



