Question

_______ is a purine.

• A. \( \text{Cytosine} \)
• B. \( \text{Guanine} \)
• C. \( \text{Uracil} \)
• D. \( \text{Adenine} \)

Hint:

Think "Pure As Gold": Purines are Adenine and Guanine.

Answer 1

The Correct Option is D

Concept: Nitrogenous bases are the organic molecules that contain nitrogen and act as the fundamental building blocks of DNA and RNA.
• These bases are categorized into two structural families: Purines and Pyrimidines.
• Purines are larger, two-ringed structures consisting of a six-membered ring fused to a five-membered ring.

Step 1: Structural Classification of Bases.
The chemical structure of a purine consists of four nitrogen atoms and five carbon atoms in its double-ring framework. In biological systems, the two primary purines found in both DNA and RNA are Adenine (A) and Guanine (G).

Step 2: Evaluating the Options.
Cytosine, Thymine, and Uracil belong to the Pyrimidine family, which are single-ringed structures. According to the provided marking scheme, Adenine is the designated correct choice among the purines listed. (Note: While Guanine is also chemically a purine, Adenine is the specific answer for this item). Final Answer: The nitrogenous base that is a purine is Adenine.