162 CHEMISTRY OF PLANT LIFE 



THE NUCLEIC ACIDS 



The nuclei of cells are composed almost wholly of complex 

 organic salts, in which proteins constitute the basic part and 

 nucleic acids the acid part. These salts, or esters, are known under 

 the general name " nucleoproteins." The composition of the 

 proteins is discussed in detail in the following chapter, and it seems 

 desirable to present a brief discussion of the constitution of the 

 nucleic acids here; although they are essentially acids rather than 

 vegetable bases. 



The nucleic acids are complex compounds consisting of a 

 carbohydrate, phosphoric acid, two purine bases, and two pyri- 

 midine bases. So far as is known, all animal nucleic acids are 

 identical and all plant nucleic acids are identical; but those of 

 plant origin differ from those found in animal cells in the character 

 of the carbohydrate and that of one of the pyrimidine bases which 

 are present in the molecule, as shown in the following tabulation 

 of their composition: 



Animal nucleic acid Plant nucleic acid 



Phosphoric acid Phosphoric acid 



Hexose (levulose) Pentose (d-ribose) 



Guanine Guanine 



Adenine Adenine 



Cytosine Cytosine 



Thymine Uracil 



The structure of the plant nucleic acid may be represented 

 by the following formula : 



OH 



O=P O carbohydrate-guanine group 



O 

 O P O carbohydrate-adenine group 



O 



=P O 

 



carbohydrate-uracil group 



O=P O carbohydrate-cytosine group 

 OH 



