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Question #44537

Difficulty: 8/10 | 🟢 Free

The Question

A biochemist is investigating the osmotic pressure (π\pi) of a tetrameric protein solution at 300 K300\text{ K}. In its native folded state, the protein behaves as an ideal solute with a molar mass Mnative=1.0×105 g mol−1M_{native} = 1.0 \times 10^5\text{ g mol}^{-1}. Upon the addition of a chemical denaturant, the protein completely dissociates into four identical unfolded monomeric chains. The osmotic pressure is measured against a dialysate containing the exact same concentration of denaturant, ensuring only the protein contributes to the measured π\pi.

Due to the massive increase in the hydrodynamic radius and excluded volume upon unfolding, the denatured monomers exhibit non-ideal behavior. The osmotic pressure of such macromolecular solutions follows the virial expansion: πC=RT(1M+BC)\frac{\pi}{C} = RT \left( \frac{1}{M} + BC \right) where CC is the protein concentration in g L−1\text{g L}^{-1}, MM is the molar mass of the kinetic solute particle, and BB is the second virial coefficient. For the denatured state, B=3.6×10−5 L mol g−2B = 3.6 \times 10^{-5}\text{ L mol g}^{-2}.

Calculate the ratio of the osmotic pressure of the denatured state to the native state (πdenπnat\frac{\pi_{den}}{\pi_{nat}}) at a protein concentration of C=10 g L−1C = 10\text{ g L}^{-1}.

Options

  • A.

    4

  • B.

    36

  • C.

    37

  • D.

    40

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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

Osmotic Pressure vs Diffusion|Protein Denaturation Specificity

Why This Question Is Tricky

Common Mistakes

This problem tests the limitations of van't Hoff's ideal osmotic pressure law (π=iCRT\pi = iCRT) when applied to macromolecules.

Students often fall into two traps: (1) They account for the dissociation into 4 monomers but ignore the non-ideal excluded volume caused by unfolding (yielding a ratio of 4, Option A). (2) They account for the virial coefficient BB but forget that denaturation also cleaves the tetramer into monomers, incorrectly using the native molar mass 10510^5 in the denatured calculation (yielding a ratio of 37, Option C).

The true physical chemistry of protein denaturation requires accounting for both the change in the kinetic unit's molar mass and the massive increase in the hydrodynamic radius (Flory-Huggins theory / Virial expansion).

Quick Facts About This Question

Question Information

SubjectChemistry
ChapterSolutions - Class 12
ConceptOsmotic Pressure vs Diffusion
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree