36 Nature of the Genetic Material 



certain conditions and after breakage of the hydrogen bonds the 

 molecule can fold up into a more compact form. Of course nobody 

 knows whether these properties apply also to the molecule within 

 the chromosome alone. 



From these basic and many additional facts, conclusions have 

 been drawn in regard to the role of the DNA molecule in the 

 chromosome, apart from simply identifying it with the gene. It has 

 been suggested that it acts as a template on which the peptide 



o^ o' 



S ^ N >— NH, 



'^^' y\ V^/^ Adenine^ 



HO O 



CM. ^O. 



p 



y\ NH 



V N 



\ 



.x>-^ 



Thymine 



OH 



Guanine 



Fig. 4. Constitution of a short section of DNA chain with pentose sugars, phos- 

 phates, and attached bases. (From Butler, 1952.) 



chains composing the protein molecules (assumed to be the real 

 genie part) are laid down at the time of self -duplication of the 

 protein chain. Quoting from Butler (1952), it was suggested by 

 Caldwell and Hinshelwood that if two of the entities present in the 

 nucleic acid are involved in the formation of each amino acid residue, 

 the permutations and combinations of four bases and one sugar taken 

 two at a time provide the necessary number of possibilities. The 

 general idea is that the DNA is not the self-duplicating unit of 

 heredity but only a support for the proteins, which are the actual self- 

 duplicating units, though the DNA scaflFolding seems indispensable 



