Question

Double hydrogen bond occurs in DNA between

• A. Adenine and thymine
• B. Uracil and thymine
• C. Adenine and guanine
• D. Thymine and cytosine

Answer 1

Answer: (A)

Adenine and thymine

The nitrogenous bases are purines and pyrimidines. The purines are adenine and guanine. The pyrimidines are thymine and cytosine. The purines are double ring structure while the pyrimidines are the single ring made up of carbon and nitrogen. Purines pair with the pyrimidines by hydrogen bonds. Adenine pairs with thymine by two hydrogen bond while the cytosine pairs with the guanosine by three hydrogen bonds.

So, the correct answer is option A.