154 



NUCLEOPROTEINS, NUCLEIC ACIDS, RELATED SUBSTANCES 



Products from ribo- 

 nucleic acid 



Adenine, guanine 

 Cytosine, uracil 

 v-Ribose 

 Phosphoric acid 



Products from desoxy- 

 ribonucleic acid 



Adenine, guanine 



Cytosine, 5-methylcystosine, thymine 



D-Desoxyribose 



Phosphoric acid 



Classification of 

 products 

 Purine 

 Pyrimidine 

 Pentose 

 Acid 



Four of the products are found in both kinds of nucleic acid. The dis- 

 tinguishing products are uracil and D-ribose for ribonucleic acid and 

 thymine, 5-methylcytosine and D-desoxyribose for the other type. The 

 sugars are the products from which the terms ribonucleic acid (RNA) 

 and dcsoxyribonucleic acid (DNA) are derived.^ It was at one time 

 believed that ribonucleic acid was found only in plants and dcsoxyribo- 

 nucleic acid only in animal cells. This view is incorrect, and it now 

 appears probable that all cells contain both types. The dcsoxyribonucleic 

 acid seems to be most abundant in the nucleus of the cell, and the ribo- 

 nucleic type to be preponderant in the cytoplasm surrounding the nucleus. 



Purines and pyritnidines 



The structural formulas of the purines are given below: 



(1) N=CH (6) 



I I 

 (2)HC(5)C— NH (7) 



CH(8) 

 // 



(3) N— C-N 



(4) (9) 



Purine 

 (synthetic base) 



N=C— NHj 



I i 



HC C-NH 

 \ 



// 



N— C-N 



Adenine 



CH 



N=C— OH 



I I 

 HoNC C-NH 

 \ 



CH 

 // 

 N— C-N 



Guanine 



N=C— OH 

 I I 

 HC C-NH 



C-N 



Hypoxan thine 



N=C— OH 

 I I 

 HO-C C-NH 

 \ 



// 



N— C-N 



Xanthine 



CH 



^Research workers use the terms pentosenucleic acid (PNA) and desoxypentose- 

 nucleic acid (DNA) as general terms and limit the more specific names to nucleic 

 acids where the sugars have been definitely established as ribose (in yeast, liver, and 

 tobacco mosaic virus) and desoxy ribose (in calf thymus). This cautious attitude 

 is probably desirable for the research worker, but since ribose and desoxyribose are 

 the usual sugars found in nucleic acids, it is less complicated for the beginning student 

 to start with the particular name and proceed to the general term Avhen it becomes 

 necessary. 



