Nucleic Acids and Nucleoproteins 



61 



decrease in particle size, but the relation between it and 

 molecular weight changes is not a simple one. 



2 DOSEXlO"S 



Fig. 1. Effect of 15 mcv electrons on solid and aqueous DNA. (Measurements 

 by R. H. Pain on materials irradiated by Prof. J. Rotblat.) 



Chemical changes can also be observed in aqueous solutions 

 although large doses of radiation are required to produce 

 easily measured effects. Among the reactions which have 



H2O 



/ (OH 

 PO4/ ^ 



■'H)© 



? 



'N. 



OH 



O, 



'C- 



•'CH2-CH ChJKI-C .' N 



N-C 



OH 



\_ / ; ;\' / 



^tJ® '"^^^ 'l^H, -'H) 



Fig. 2. Some chemical effects of radicals on 

 DNA in aqueous solution. 



been observed (Fig. 2) are (1) deamination of the bases; 

 (2) dehydroxylation ; (3) fission of the sugar-base linkage and 

 in some cases breakage of the pyrimidine ring; (4) oxidation 

 of the sugar moiety and (5) breakage of the nucleotide chains 



