122 GENERAL BIOCHEMISTRY 



These nucleosides are esterified with phosphoric acid in the nucleo- 

 tides. Any of the available hydroxyl groups could participate and do, 

 at least under special conditions. In the nucleic acids, however, the 

 ester bonds probably involve only the hydroxyl groups of carbons three 

 and five of either ribose or deoxyribose. Adenylic acid is a typical 



CHaOPOg 



adenosine-5'- phosphate 

 adenyhc acid (from muscle) 



nucleotide. The nomenclature of all these related compounds may be 

 summarized thus: 



These and the other closely related nucleotides make up the nucleic 

 acids. In addition, some of them have exceedingly important inde- 

 pendent metabolic roles, one being the transfer of chemical energy. 

 Moreover, there are other similar nucleotides performing related meta- 

 bolic functions. These important considerations are developed in 

 later chapters. 



Nucleic Acids 



The natural condensation products of nucleotides reach macro- 

 molecular dimensions, are called nucleic acids, and are found in all 

 ordinary cells. They are associated in turn with protein in nucleo- 

 proteins. Although much is still unknown, a start has been made to- 

 ward understanding the structures of the nucleic acids. 



In the first, place these compounds fall into two groups, those con- 

 taining ribose and those containing deoxyribose. These classes are 

 known, respectively, as ribonucleic acids or RNA and deoxyribonucleic 

 acids or DNA. When the sugar has not been positively identified, it is 

 customary to use the terms pentosenucleic and deoxypentosenucleic 

 acids, just in case the sugar turns out to be another pentose. So far as 



