Question

Which one of the following is not a pyrimidine base?

• A. Thymine/T
• B. Guanine/G
• C. Cytosine/C
• D. Uracil/U

Answer 1

The correct option is B

Guanine/G

The correct option is option (B):

Explanation of the correct option:

1. There are two nitrogen bases which are found in the nucleic acids namely purines and pyrimidines.
2. Purines are nitrogen ring bases with two carbons, whereas pyrimidines have a one-carbon nitrogen ring base.
3. Guanine is a purine that has two-ring molecular structure.

Explanation of the incorrect option:

Option (A):

Thymine is a pyrimidine and it is found only in DNA.

Option (C):

Cytosine is a pyrimidine nitrogen base which is found in both DNA and RNA.

Option (D):

Uracil is a pyrimidine nucleobase that occurs naturally in RNA.

Final answer: The nitrogenous base guanine/G is not a pyrimidine.