Nucleotides and nucleic acids
Publisher Summary
This chapter discusses nucleotides and nucleic acids. The nucleotides, which consist of three parts, namely, a nitrogenous base, a pentose sugar, and a phosphate radical, are a very important group of compounds as one or more of them is involved in virtually every biochemical process. The adenosine di- and triphosphates play an essential part in cellular energy exchanges that have a nucleotide-type structure as do many of the coenzymes. Nucleotides constitute the monomeric units of which the nucleic acids are composed; this means that nucleic acids are polynucleotides. The nucleic acids are of two types—deoxyribonucleic acid (DNA) and ribonucleic acid (RNA)— and are responsible for directing the synthesis of proteins. They specify the unique sequence of amino acids in any particular protein and, consequently, should be regarded as primordial molecules on whose existence that of the proteins depends. However, as the synthesis of the nucleic acids depends on enzymes that are themselves proteins, this poses the fundamental evolutionary question as to which came first—the biochemical version of the problem of the chicken and the egg. In addition to their role in protein synthesis, nucleic acids transmit genetic information from the parent to offspring and the entire range of inherited characteristics of any organism is believed to be defined in terms of the deoxyribonucleic acid that its cells contain.
Nucleic acid components



DNA and RNA both contain the two substituted purines adenine (6-aminopurine) and guanine (2-amino-6-oxypurine). Small amounts of other bases including hypoxanthine and a variety of methylated purines and pyrimidines are found in certain types of RNA (page 299).


Phosphoric acid is released on acid hydrolysis of both DNA and RNA.
Nucleosides and nucleotides
Table 9.1
Some nitrogenous bases and their derivatives
Nitrogenous base | Type | Substituents | Nucleoside | Nucleotide |
Adenine | Purine | 6-amino | Adenosine | Adenylic acid |
Guanine | Purine | 2-amino-6-hydroxy | Guanosine | Guanylic acid |
Hypoxanthine | Purine | 6-hydroxy | Inosine | Inosinic acid |
Cytosine | Pyrimidine | 2-hydroxy-4-amino | Cytidine | Cytidylic acid |
Thymine | Pyrimidine | 2,4-dihydroxy-5-methyl | Thymidine | Thymidylic acid |
Uracil |