Purines have what kind of ring structure?

• A. Single ring
• B. Double ring
• C. No ring
• D. Triple ring

Answer: (B)

Purines have a double-ring, bicyclic structure. They are built from a six-membered ring fused to a five-membered ring, forming a larger planar heterocycle. This distinguishes them from pyrimidines, which contain a single six-membered ring. In DNA and RNA, the two-ring purines (adenine and guanine) pair with the single-ring pyrimidines (thymine/uracil and cytosine) to help maintain the regular width of the helix. So the correct description is that purines contain two fused rings.