Question

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

• A. A
• B. B
• C. C
• D. D

Hint:

Biological nitrogenous bases (Uracil, Thymine, Guanine, Cytosine) are generally represented in their most stable "keto" (lactam) form in the context of DNA and RNA.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Uracil is a nitrogenous base found in RNA. It can exist in several tautomeric forms (lactam and lactim), but one specific form is biologically active and present in the RNA structure.
Step 2: Detailed Explanation:
Uracil (2,4-dioxopyrimidine) exists primarily in the diketo form (lactam form) under physiological conditions and in the structure of RNA. This form allows for specific hydrogen bonding with adenine.
Option (A) represents the diketo form with two \(C=O\) groups and two \(NH\) groups in the ring.
Options (B), (C), and (D) represent various enol (lactim) tautomers which are less stable and not the predominant form in nucleic acids.
Step 3: Final Answer:
The diketo form shown in Option (A) is the one present in RNA.