Which of the following nitrogenous bases is a double-ring purine derivative found in both DNA and RNA?
Answer and explanation
Correct answer: B. Adenine
- Step 1: Nitrogenous bases in nucleic acids belong to two chemical families: bicyclic purines and monocyclic pyrimidines.
- Step 2: Purines consist of fused six-membered pyrimidine and five-membered imidazole rings; the two universal biological purines are Adenine and Guanine.
- Step 3: Cytosine, Uracil, and Thymine are six-membered single-ring pyrimidines.
Answer
Adenine.
Why not the others: Cytosine is a single-ring pyrimidine present in DNA and RNA; Uracil is a single-ring pyrimidine found exclusively in RNA; Thymine (5-methyluracil) is a single-ring pyrimidine found in DNA.
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