120 GENERAL BIOCHEMISTRY 



NUCLEIC ACIDS AND NUCLEOPROTEINS 



Nucleoproteins 



These natural macromolecules are made up of two parts. One part 

 is protein and the other nucleic acid. The two components are at- 

 tached, but the nature of the bonds is not fully understood. The 

 nucleic acids, as the name suggests, are acidic compounds and exist 

 as anions at physiological pH values. On the other hand, the protein 

 components of the nucleoproteins seem to be of the histone type and 

 carry net positive charges. Thus salt formation between the nucleic 

 acid and protein is a strong possibility, but there may be other forces 

 of combination as well. At any rate, though it is common to speak 

 of and study nucleic acids by themselves, it is probable that they do 

 not exist independently in cells. Rather, the nucleic acids are asso- 

 ciated with proteins in their natinal state. 



The chemistry of the nucleic acids and their components is outlined 

 below, but even less is known of the chemistry of the associated pro- 

 teins than of proteins in general. Isolations are difficult and careful 

 fractionation studies lacking, so that it is not clear whether the nucleo- 

 proteins from a single source are based on one or on a multiplicity of 

 proteins. Probably there are many different protein components since 

 there are believed to be many different nucleic acids and nucleoproteins. 

 The histone (or histones) involved does have an exceptionally high 

 content of the basic amino acids arginine and lysine. 



Nucleoproteins may be regarded as aggregates of successively smaller 

 subunits. These various levels of composition may be classified as fol- 

 lows, proceeding in the direction of the smallest components: 



Nucleoproteins 



Nucleic acids + Proteins 



i 

 Nucleotides 



i. 

 Nucleosides + Phosphate 



Ribose or Pyrimidine or 



deoxyribose purine bases 



Nucleotides 



These compounds consist of organic bases and phosphoric acid 

 condensed with particular pentoses. The sugars known to be involved 

 in some nucleic acids are ribose and deoxyribose (see page 62), 



