NUCLEIC ACID 



383 



Guanosine (a nucleoside) 

 HOs 



= P— O 



Phosphoric acid 



Guanine nucleotide 

 The bases uracil and cytosine are derived from pyrimidine, 

 a substance which does not itself occur naturally ; the re- 

 lationship of these substances to uric acid will be seen from 

 a comparison of the formulae : — 



NH- 



I 



-co 



1 



C— NH\ 



CO 



NH— C— NH-^ 

 Uric acid 



N=CH 



CHCH 



'I J^ 

 N— CH 



NH- 



I 

 CO 



-CO 



N-- 



-C— NH, 



H 



NH— CH 



Uracil 



CO CH 



I II 



NH— CH 



Cytosine 



Pyrimidine 



Jones and Perkins have some doubt as to whether uracil 

 nucleotide is a true constituent of plant nucleic acid, and 

 suggest that it is a secondary product arising from the cytosine 

 nucleotide ; they accordingly think that the distinction between 

 animal and plant nucleic acids will in the future not be so 

 definitely drawn. 



In attempting to reconstruct the formula of nucleic acid 

 from the constituent nucleotides, two possible configurations 

 present themselves according as they are linked through the 

 phosphoric acids or through the carbohydrate residues as is 

 outlined below : — 



HO 



HO 



\ 



o=p— o 



/ 



o 



\ 



o=p— o 



/ 



o 



\ 



0:=P— O . 



/ 



o 



\ 



o=p— o . 



/ 



HO 



I. 



or 



0=P— O . 



/ 

 HO 

 HO 



\ 



0:=P— O . 

 / 



HO 

 HO 



\ 



o=p— o . - 



/ 



HO 

 HO 



\ 

 ^P— O . - 



/ 



HO 



O 



II. 



