Question

Pyrimidines differ from purines in their basic structural feature. Which statement is correct?

Options

• Pyrimidines and purines differ only in the atoms composing their rings

• Pyrimidines have a single-ring structure while purines have a double-ring structure

• Both pyrimidines and purines have identical ring structures

• Pyrimidines have a double-ring structure while purines have a single-ring structure

Answer 1

Purines (Adenine and Guanine) have a double-ring structure consisting of a six-membered ring fused to a five-membered ring. Pyrimidines (Cytosine, Thymine, and Uracil) have a single six-membered ring structure. This structural difference affects their pairing properties and chemical behavior in nucleic acids.