In DNA two types of nitrogenous base are formed :- theses are -(1) purine – is a double ring structure present in the form of adnine and guanine. (2) pyrimidine – is a single structure present in the form of cytosine and thymine.
There are 4 Nitrogenous bases present in the DNA :-
Adenine,Guanine,Thymine and Cytosine.
Adenine and Guanine are classified as Purines while Thymine and Cytosine are classified as Pyrimidines.