JEE Main · 2021 · 27 Aug 2021 · Shift 1 · Biomolecules

Out of following isomeric forms of uracil, which one is present in RNA?

(A)(see structure)
(B)(see structure)
(C)(see structure)
✓ Correct
(D)(see structure)

Answer: (C)

Solution

In nucleic acids uracil exists in the lactam, or diketo, tautomer, the form that base-pairs with adenine. This tautomer carries carbonyl groups at

C_{2}

and

C_{4}

and

N - H

bonds at

N_{1}

and

N_{3}

, and it is more stable than the lactim (enol) forms because amide resonance is stronger than that of the hydroxyl tautomers. The isomer present in RNA is the diketo form of uracil.

JEE Main · 2021 · 27 Aug 2021 · Shift 1 · Single correct option

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