Question

Purines bond with __________ by forming hydrogen bonds.

• A. only purines
• B. both purines and pyrimidines
• C. either purines or pyrimidines
• D. only pyrimidines

Answer 1

The correct option is D only pyrimidines

Purines always bond with pyrimidines by forming hydrogen bonds. The two bases, adenine (A) and guanine (G) are purines while cytosine (C), thymine (T) and uracil (U) are pyrimidines. Adenine always bonds with thymine by two hydrogen bonds (A=T) in a DNA molecule. Whereas in an RNA molecule, adenine pairs with uracil by two hydrogen bonds (A=U). Guanine bonds with cytosine by three hydrogen bonds (G$\equiv$C) in both DNA and RNA.