STRUCTURE OF THE NUCLEIC ACIDS 181 



Yeast nucleic acid is known to consist of the following four mono- 

 nucleotids. 



H(X 

 O = P O.C 6 H8O 3 .C 6 H4N5 



/ 



HO/ 



Adenine mononucleotid 



HCk 

 O = P O.C 5 H 8 O 3 .C4H 3 N 2 O2 



HO/ 



Uracil mononucleotid 



HOv 



O = 



HO/ 



Cytosine mononucleotid 



HOv 

 O = P O.C 5 H8O3.CBH4N 5 O 



HO/ 



Guanine mononucleotid 



We know, also, that these mononucleotids are united to one another 

 in the order indicated, for when yeast nucleic acid is heated with 

 ammonia it yields adenine-uracil dinucleotid, so that the constituent 

 mononucleotids of this substance must be united together in the 

 unaltered nucleic acid molecule. On the other hand, when carefully 

 heated with acids, yeast nucleic acid splits off adenine and guanine 

 mononucleotids leaving uracil-cytosine dinucleotid. It is evident, 

 therefore, that the uracil and cytosine mononucleotid radicals are 

 united to one another in the yeast nucleic acid molecule, and that the 

 adenine and guanine mononucleotids form the extremities of the 

 molecule. 



Now the Adenine Uracil Dinucleotid might conceivably consist of 

 two mononucleotids united by their phosphoric acid radicals, or they 

 might be united in some other manner. If they were united by their 

 phosphoric acid molecules, at least one of the hydroxyl-groups of the 

 phosphoric acid radicles would disappear by neutralization. The 

 total number of available hydroxyl-groups contained in the two 

 phosphoric acid radicals is four, so that the maximum number of 

 molecules of any base that adenin-uracil dinucleotid could combine 

 with would be four. If any hydroxyl-groups were neutralized by 

 union of phosphoric acid radicals with each other or with other parts 

 of the associated mononucleotid the free hydroxyl-groups would be less 

 than four, and the dinucleotid would, in consequence, neutralize less 

 than four molecules of a base. Now adenine-uracil dinucleotid forms 

 a compound with four molecules of Brucine. It follows, therefore, that 



