60 



E. MARKHAM 



quantity which should be detectable in virus labeled with radioactive 

 phosphate (Keddi and Knight, 1957; Matthews and Smith, 1957). 



Z). Deoxyribonucleic Acids 

 The deoxyribonucleic acids, which differ from the ribonucleic acids by 

 not having an — OH group at C-2' of the nucleoside residues, are in conse- 

 quence of this stable to alkali and also to ribonuclease. On the other hand, 

 the purine glycosidic link is extremely unstable to acid, and splitting of 

 this link gives rise to an aldehydic function at C-l', which is followed by 

 jS-ehmination at C-3'. The products of acid treatment (60°C,, 0.1 N-HCl, 

 10 min. or more) are thus chains of the type p — nA — p, where n is an integral 

 number, and A any pyrimidine nucleoside (or mixture of the same). The 

 determination of the structure of the small polynucleotides is quite easily 

 accomplished using specific enzymes. 



220 240 260 280 300 320 

 (m/i) 

 Fig. 4. Absorption spectrum of a typical ribonucleic acid, at 20°C. in water at pH 7. 



E. Physical Properties of the Nucleic Acids 

 The most spectacular property of the nucleic acids is their extremely 

 high and specific ultraviolet light absorption, which is occasioned by their 

 purine and pyrimidine constituents (Fig. 4). Oddly enough, the light absorp- 

 tion of a nucleic acid is much smaller than that of its constituent nucleotides 



