Question

The compound 'A' is a complementary base of _________ in DNA strands. 

 

• A. Guanine
• B. Adenine
• C. Cytosine
• D. Uracil

Hint:

A simple mnemonic for DNA base pairing is "At The Grand Canyon" (A pairs with T, G pairs with C). Remember that A and G are the larger purine bases, while T and C (and U in RNA) are the smaller pyrimidine bases.

Answer 1

The Correct Option is B

First, we must identify the given compound 'A'. The structure shown is a pyrimidine base with a methyl group at the 5th position and two carbonyl groups. This is the structure of Thymine (T).
In DNA, the nitrogenous bases form specific pairs between the two strands, held together by hydrogen bonds. This is known as complementary base pairing.
The rules for base pairing in DNA, established by Watson and Crick, are:
1. Adenine (A), a purine, always pairs with Thymine (T), a pyrimidine, via two hydrogen bonds.
2. Guanine (G), a purine, always pairs with Cytosine (C), a pyrimidine, via three hydrogen bonds.
Since compound 'A' is Thymine (T), its complementary base in a DNA strand is Adenine (A).
Uracil is the base that replaces Thymine in RNA and pairs with Adenine.