Question

Which nitrogenous bases are classified as pyrimidines, characterized by their single-ringed structure?

Options

• Adenine and Thymine

• Guanine and Cytosine

• Cytosine and Thymine

• Adenine and Guanine

Answer 1

Pyrimidines are nitrogenous bases with a single-ringed structure. The two pyrimidines in DNA are cytosine (C) and thymine (T). They pair with purines (adenine and guanine, which have double-ringed structures) to maintain uniform helix diameter. This complementary pairing of purine-pyrimidine combinations ensures consistent spacing in the DNA double helix.