Question

Given below are two statements:
Statement I: Hydrolysis of a peptide bond takes place rapidly because the activation energy of peptide bond hydrolysis is high
Statement II: Hydrolysis of the peptide bond is an exergonic reaction
In the light of the above statements, choose the most appropriate answer from the options given below

• A. Both Statement I and Statement II are true
• B. Both Statement I and Statement II are false
• C. Statement I is true but Statement II is false
• D. Statement I is false but Statement II is true

Hint:

Peptide Bond Stability: Thermodynamically unstable (hydrolysis is exergonic, $\Delta G < 0$) but Kinetically stable (high $E_a$ prevents rapid breakdown without proteases).

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Thermodynamics vs kinetics of peptide bonds: peptide bond hydrolysis is thermodynamically favorable (exergonic) but kinetically extremely slow due to high activation energy.
Key Formula or Approach:
\[ \text{Peptide} + \text{H}_2\text{O} \longrightarrow \text{Amino Acids}, \quad \Delta G^{\circ\prime} \approx -10\text{ to } -15\text{ kJ/mol (Exergonic)} \]

Step 2: Detailed Explanation:
1. Statement I: Peptide bonds possess partial double-bond character ($40\%$ resonance stabilization) and have a very high activation energy barrier ($E_a \approx 80-100\text{ kJ/mol}$). Consequently, uncatalyzed hydrolysis in neutral aqueous solution is exceptionally slow (spontaneous half-life exceeds 500 to 1,000 years). Thus, Statement I is false.
2. Statement II: Thermodynamically, the free energy change of peptide bond hydrolysis is negative ($\Delta G^{\circ\prime} < 0$), releasing free energy (exergonic reaction). Thus, Statement II is true.

Step 3: Final Answer:
Therefore, Statement I is false but Statement II is true, corresponding to option (D).