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Question #44956

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The Question

Consider the nucleoside 2'-deoxyguanosine dissolved in an aqueous buffer at pH 7.4 and 298 K. The system is allowed to reach thermodynamic equilibrium. Which of the following statements accurately describes the dynamic structural isomerism and stereochemistry of the molecule under these conditions?

Options

A.
The guanine moiety exhibits lactam-lactim tautomerism, and the deoxyribose moiety undergoes continuous anomerization between $\alpha$ and $\beta$ forms via a transient open-chain aldehyde.
B.
The guanine moiety exhibits lactam-lactim tautomerism, while the deoxyribose moiety remains stereochemically locked in the $\beta$ -anomeric configuration due to the absence of a free hemiacetal hydroxyl group.
C.
The N-glycosidic bond undergoes reversible heterolysis, allowing both epimerization at the C-2' position of the sugar and tautomerization of the guanine base.
D.
The molecule exists exclusively in the keto (lactam) form with a fixed $\alpha$ -anomeric configuration, as tautomerization is sterically hindered by the sugar ring.

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Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Mechanism_Trap

Don't get tricked by the process! Learn the mechanical traps used in competitive exam questions.

Concepts Behind This Question

Epimerization vs Anomerization|Nitrogenous Base Keto-Enol Tautomerism|Base Pairing Stability

Why This Question Is Tricky

Common Mistakes

This question tests the critical distinction between the reactivity of hemiacetals (free sugars) and acetals/N-glycosides (nucleosides).

The primary trap is the assumption that the dynamic tautomerism of the nitrogenous base implies a similarly dynamic sugar ring.

Students often erroneously conflate the mutarotation of free glucose with the behavior of ribose in DNA/RNA.

The 'hidden variable' is the kinetic stability of the N-glycosidic bond at physiological pH, which permanently locks the anomeric carbon in the $\beta$ -configuration, preventing the open-chain intermediate required for anomerization.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Biomolecules - Class 12
Concept	Epimerization vs Anomerization
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free