1) Purines contain only four ring nitrogen atoms while Pyrimidines contain only two nitrogen ring atoms
2) Purines contain two heterocyclic rings while Pyrimidines contain one heterocyclic ring
Explanation:
Purines and Pyrimidines are two classes of nitrogenous bases that make up nucleic acids. They are both heterocyclic aromatic compounds which contains nitrogen atoms in their structure. Although, they are similar but have distinct features namely:
Purines are ring molecules which consists of four (4) nitrogen atoms in their aromatic structure. They are structures with two heterocyclic rings consisting of five (5) carbon and four (4) nitrogen atoms. Adenine and Guanine are the purines in nature.
On the other hand, Pyrimidines are another ring molecules consisting of two (2) nitrogen atoms in their aromatic structure. Their only ring i.e. 1, is also heterocyclic in nature and contains four (4) carbon and two (2) nitrogen atoms. Cytosine, Thymine and Uracil are the pyrimidines.
