Question

Nitrogenous bases in DNA are classified into two categories based on ring structure. Which bases belong to the purine class?

Options

• Guanine and Thymine

• Adenine and Cytosine

• Cytosine and Thymine

• Adenine and Guanine

Answer 1

Purines are nitrogenous bases with a double-ringed structure. The two purines found in DNA are adenine (A) and guanine (G). Pyrimidines, which have a single-ringed structure, are cytosine (C) and thymine (T). Purines always pair with pyrimidines in the DNA double helix.