DNA molecule contains 4 bases whose structure are shown below. One of the structures is not correct, identify the incorrect base structure.
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Answer
(4) [figure]
Solution
DNA bases: thymine and cytosine (pyrimidines), adenine and guanine (purines)
(A): 5-methyl pyrimidine-2,4-dione ⇒ (A) is thymine (correct)
(B): 4-amino pyrimidin-2-one ⇒ (B) is cytosine (correct)
(C): 6-amino purine ⇒ (C) is adenine (correct)
(D): 2-amino-6-oxopurine carries CH3 at C-8 ⇒ (D) is not guanine (incorrect)
∵ guanine has H at C-8 (no methyl group):
[figure]
Answer: (4)