Nucleic acid are polymers of nucleotides and hence may be called polynucleotide sequences. Complete hydrolysis of nucleic acids yields heterocyclic nitrogenous bases, five carbon sugars and phosphoric acid molecules, while partial hydrolysis yields nucleotide residues only. A scheme of hydrolysis is given below.
    The two types of nucleic acids, DNA and RNA differ in their molecular organization and chemical composition. DNA contains four types of nitrogenous bases –adenine, thymine,cytosine, guanine–and deoxyribose sugar, whereas RNA contains uracil in place of thymine, besides other bases and the sugar is ribose. The bases can be divided into two categories on the basis of their ring structures, namely pyrimidines and purines.