Nitrogenous bases The bases are nitrogen containing molecules having the chemical properties of a base (a substance that accepts H + ion or proton in solution). DNA and RNA both have four bases (two purines and two pyrimidines) in their nucleotide chain. Two of the bases, Adenine (A) and Guanine (G) have double carbon–nitrogen ring structures and are called purines. The bases, Thymine (T), Cytosine (C) and Uracil (U) have single ring structure and these are called pyrimidines.
Thymine is unique for DNA, while Uracil is unique for RNA.