# DBT JRF 2022 — Question 20

Exam: DBT JRF 2022 · Section: B · Topic: Biochemistry › Protein Folding & Thermodynamics · Difficulty: Medium

## Question

A protein completely unfolds in 8 M Urea. The stability of the folded state in water is calculated to be 8 kCal/mole at 25°C. What is the likely ΔG of the following reaction in 8 M Urea? A(native) → A(unfolded)                                                                                                                                                                                                                                                                                                                                                              Choose the correct answer :

## Options

- **A.** Zero
- **B.** Less than zero
- **C.** $$8^2$$
 kcal/mole
- **D.** 8 kcal/mole

## Answer

Option B

## Explanation

Thermodynamics of protein unfolding in 8M urea: Given: • Stability of folded state in water: $\Delta G_{\text{folding}} = +8\,\text{kcal/mol}$ (positive = folded state is more stable, unfolding is unfavourable in water) Reaction of interest: $A_{\text{native}} \rightarrow A_{\text{unfolded}}$ in 8M urea. • In 8M urea, the protein COMPLETELY unfolds — meaning this reaction proceeds spontaneously. • For a spontaneous reaction: $\Delta G < 0$ Therefore, $\Delta G$ for unfolding in 8M urea is LESS THAN ZERO (negative). Note: The magnitude is not exactly −8 kcal/mol because urea changes the free energy landscape (it stabilises the unfolded state by disrupting hydrophobic interactions and H-bonds). Answer: Less than zero (Option 2).

Source: https://mypyqbuddy.com/questions/a-protein-completely-unfolds-in-8-m-urea-6a104cd5920734408bc0c723