Polynucleotides are called nucleic acids. Each nucleotide is made up of three parts, i.e, a pentose sugar, a heterocyclic nitrogenous base and phosphoric acid. Depending upon the nature of sugar whether, ribose or deoxyribose, nucleic acids are called RNA and DNA respectively. In all, there are five nitrogenous bases, two of which are purines while the remaining three are pyrimidines. Out of these five bases, each type of nucleic acid has four of them.
In nucleic acids, the nucleotides are linked to one another through: