Nucleic Acids
These are protein-bound polymers that are essential in many biological processes. They perform such functions as directing the syntheses of proteins in living cells and constitute the chemical basis of heredity [56, 57]. The polymers are polyphosphate esters of sugars that contain pendant heterocyclic amines, called “bases”:
There are two principle types of nucleic acids with two different sugars. One is D-2-deoxyribose found in deoxyribonucleic acid (DNA):
The other one D-ribose is found in ribonucleic acids (RNA):
The sugars are in the furanose form. They are linked through the hydroxyl groups on carbons 3 and 5 asphosphate esters. The heterocyclic amine “bases” are attached at carbon 1, replacing the hydroxyl group. A sugar molecule with a base attached to it is referred to as a nucleoside:
A nucleoside esterified with phosphoric acid is called a nucleotide:
All the heterocyclic amines that occur in nucleic acids (DNA and RNA) are derivatives of either pyrimidine or purine. These are:
The naming of nucleosides depends upon the sugars. Thus, adenine attached to ribose is called adenosine. When it is attached to deoxyribose, it is called deoxyadenosine. Hydrolysis of nucleoproteins separates the acids from the proteins. Further hydrolysis yields the components of nucleic acids, namely sugars, bases, and phosphoric acid. The nucleic acids differ from each other, depending upon the source, in chain lengths, sequences, and distributions of bases. Just like in the proteins, the primary structure of nucleic acids is determined by partial and sequential hydrolysis.
