THE NUCLEIC ACIDS 



parent substances differ in that in the former there is a reducing carbo- 

 hydrate which produces furfural on hydrolysis (Figure i) and is thus 

 a pentose. A further difference between the two groups is found in 

 respect to the second category of constituent basic groups, the pyrimi- 

 dines, the presence of which was recognized in 1893 by Kossel and 

 Neumann. 2^ In a series of papers pubHshed in 1903, Levene^^ showed 

 that the pyrimidine cytosine was common to both plant and animal 

 nucleic acids, but that uracil was only found in the former, and thymine 

 only in the latter. Mandel and Levene,^" however, found uracil and 

 not thymine in their analysis of the nucleic acid offish eggs. In Table I 

 the main points of difference between the two types of nucleic acid are 

 summarized. The admirable reviews of Schlenk^^ and Davidson^^ 

 should be consulted for further information in the chemical field. 



TABLE I 



Pentose 



rna 



CH2OH n OH 



OH OH 

 </-Ribofuranose 



DNA 



CHpO 



2^0 



OH 



H ^ r H 



OH H 



2-Deoxy-</-ribofuranose 



Pyrimidines* 



N = C-NH2 

 I I 

 = C CH 

 I II 

 HN— CH 



HN— C = 

 I I 

 = C CH 

 I II 

 HN— CH 



Cytosine and Uracil 



HN— C = 

 I I 

 = C C-CH3 

 I II 

 HN— CH 

 Cytosine and Thymine 



NUCLEOPROTEIN WITHIN 



THE Cell 

 Turnover Rate 



Molecular Weight 

 OF Isolated Acid 



Readily Stained by 



Cytoplasm, Nucleolus 

 and Chromosomes 

 high 



10,280-23,250 

 (yeast RNA, Fletcher 



et alii^"^) 



Basic Dyes such 

 as methylene blue and 

 toluidine blue 



Chromosomes 



low: varies with mitotic rate 

 (Furst et alii^"^) 



500,000 (Signer et alii^^'') 



— 3,000,000 (Gulland 



et alii^'>») 



Methyl Green 

 and Schiff 's base 

 (after hydrolysis) 



FEULGEN REACTION 



The carbohydrate of thymonucleic acid, corresponding to the pentose 

 of yeast nucleic acid was believed by Kossel and Neumann^^ to be a 

 hexose, on the grounds that on hydrolysis laevulinic acid was formed, 



*There have been several reports of the occurrence of 5-methyl cytosine in DNA's of 

 different sources, the most recent of which is by Wyatt.^'" 



