Question

Which of the following is NOT a purine base?

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

Hint:

Purines: Adenine, Guanine.
Pyrimidines: Cytosine, Thymine, Uracil.
Purines have two rings, pyrimidines have one ring.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Nitrogenous bases are classified as purines and pyrimidines.
This classification is based on their chemical structure.

Step 2: Key Formula or Approach:
No specific formula.
Need to know the classification of nitrogenous bases.

Step 3: Detailed Explanation:
Purine bases are: Adenine (A) and Guanine (G).
Pyrimidine bases are: Cytosine (C), Thymine (T), and Uracil (U).
Thus, thymine is a pyrimidine, not a purine.
Cytosine is also a pyrimidine, but the question asks for NOT a purine.
Thymine is the correct answer.

Step 4: Final Answer:
Thymine is NOT a purine base.
Hence, the correct option is (D).