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Question #44971

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The Question

An enzyme exhibits strict 'Lock and Key' specificity towards its substrate at $298\text{ K}$ in an aqueous buffer ( $pH = 7.4$ ). Upon severe thermal denaturation at elevated temperatures, the catalytic activity drops to zero. Beyond the disruption of non-covalent interactions (hydrogen bonds and van der Waals forces), what is the fundamental stereoelectronic cause for the irreversible loss of the active site's precise three-dimensional geometry?

Options

A.
Thermal energy overcomes the rotational barrier of the $C-N$ bond (arising from $n \rightarrow \pi^*$ resonance), destroying the planar constraint of the peptide backbone and causing a collapse into a random coil.
B.
Thermal energy induces a rapid interconversion of the $\alpha$ -carbon's stereocenter from $L$ to $D$ configuration, sterically precluding substrate binding.
C.
The elevated temperature homolytically cleaves the peptide bonds, fragmenting the primary structure and eliminating the active site residues.
D.
Thermal energy disrupts the $sp^2$ hybridization of the amide nitrogen, forcing it into a rigid pyramidal $sp^3$ geometry that permanently alters the Ramachandran angles.

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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

Protein Denaturation Specificity|Peptide Bond Planarity|Enzyme Specificity 'Lock and Key'

Why This Question Is Tricky

Common Mistakes

The 'Hidden Variable' being tested is the structural consequence of the peptide bond's resonance.

Students often memorize that thermal denaturation only breaks weak non-covalent interactions (like hydrogen bonds) while leaving the covalent backbone entirely intact and rigid.

The trap is failing to recognize that the planarity of the peptide backbone is not a fixed covalent absolute, but a resonance-derived rotational barrier ( $n \rightarrow \pi^*$ ).

When thermal energy is high enough, it overcomes this barrier, allowing rotation around the $C-N$ bond.

This loss of backbone planarity is the ultimate reason the protein collapses into a random coil, permanently destroying the 'Lock and Key' active site geometry.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Biomolecules - Class 12
Concept	Protein Denaturation Specificity
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free