Multiple choice

Which of the following is a purine?

  1. Adenine

  2. Cytosine

  3. Uracil

  4. Thymine

  5. None of these
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A Correct answer
Explanation

Purines (adenine and guanine) have a double-ring structure consisting of a pyrimidine ring fused to an imidazole ring. Pyrimidines (cytosine, thymine, and uracil) have a single six-membered ring. This structural difference is fundamental to DNA and RNA structure and affects base pairing patterns.

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