MDCAT Biology MCQ #949

In the DNA double helix, Adenine pairs with Thymine. What structural characteristic defines Adenine as a purine compared to Thymine?

MDCAT Biology MCQ #949

  1. Question 1

    Q1. In the DNA double helix, Adenine pairs with Thymine. What structural characteristic defines Adenine as a purine compared to Thymine?

    • A) A single-ring heterocyclic structure
    • B) A double-ring heterocyclic structure
    • C) The presence of only three nitrogen atoms
    • D) Attachment to the phosphate group directly

    Answer: A double-ring heterocyclic structure

    Explanation: Purines (A, G) have a double-ring structure, while pyrimidines (C, T, U) have a single ring. Students often swap these counts.