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Question #44974

Difficulty: 8/10 | 🟢 Free

The Question

A biochemist is studying the thermal denaturation of a synthetic polypeptide at 310 K310\text{ K}. The polypeptide exists in a functional Native state (\ceN\ce{N}) and a Denatured state (\ceD\ce{D}), which are in rapid equilibrium. The denatured state further undergoes a secondary equilibrium to form a stable, inactive dimer aggregate (\ceA\ce{A}). The coupled equilibria are given as:

\ceN<=>DK1=0.5\ce{N <=> D} \quad K_1 = 0.5 \ce2D<=>AK2=50 M−1\ce{2D <=> A} \quad K_2 = 50 \text{ M}^{-1}

Initially, the polypeptide is prepared in a buffer such that the total monomeric concentration is [P]0=0.18 M[P]_0 = 0.18 \text{ M} (assuming 100%100\% \ceN\ce{N} initially). Once the system reaches thermodynamic equilibrium, what is the percentage of the original polypeptide that remains in the functional Native state (\ceN\ce{N})?

Options

  • A.

    33.33%33.33\%

  • B.

    66.67%66.67\%

  • C.

    50.00%50.00\%

  • D.

    16.67%16.67\%

Check Your Answer

Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Numerical_Precision

Improve calculation stamina and avoid rounding errors in high-stakes competitive examinations.

Concepts Behind This Question

Protein Denaturation Specificity|Esterification Reversibility

Why This Question Is Tricky

Common Mistakes

This question tests the student's ability to handle coupled equilibria and thermodynamic sinks, drawing a parallel to Le Chatelier's Principle and solubility precipitation.

The 'Hidden Variable' trap is twofold: First, students often calculate the degree of denaturation using only K1K_1, ignoring the secondary aggregation equilibrium (which acts as a thermodynamic sink, pulling the first equilibrium forward and yielding the 66.67%66.67\% distractor).

Second, students frequently forget the stoichiometric factor of 2 in the mass balance equation ([P]0=[\ceN]+[\ceD]+2[\ceA][P]_0 = [\ce{N}] + [\ce{D}] + 2[\ce{A}]) because \ceA\ce{A} is a dimer, leading to an incorrect quadratic formulation.

Quick Facts About This Question

Question Information

SubjectChemistry
ChapterBiomolecules - Class 12
ConceptProtein Denaturation Specificity
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree