(B) decreasing the activation energy of the reaction.
(C) decreasing product stability.
(D) increasing the activation barrier of the reaction.
Official Answer Key:
B
Step-by-Step Solution & Explanation
### **Official Solution & Step-by-Step Derivation (GATE BT 2017 Q.01)**
**1. Governing Concept & Question Classification**:
- **Section**: BT
- **Question Type**: **MCQ** (1 Mark)
- **Topic**: Biochemistry / Enzyme Kinetics (Mechanism of Catalysis & Transition State Theory)
**2. Detailed Step-by-Step Analysis**:
- According to transition state theory (Eyring-Polanyi) and classical enzymology, enzymes accelerate biochemical reaction rates by selectively binding and stabilizing the high-energy **transition state** ($X^\ddagger$).
- This selective stabilization lowers the standard free energy of activation ($\Delta G^\ddagger$):
$k = \frac{k_B T}{h} e^{-\Delta G^\ddagger / RT}$
- By decreasing the activation energy barrier ($\Delta G^\ddagger$), a significantly larger fraction of reactant molecules possess sufficient thermal energy to cross the barrier per unit time, thereby increasing the reaction rate by orders of magnitude ($10^6$ to $10^{17}$-fold).
- Enzymes do **not** alter the ground-state free energies of the substrates or products, nor do they alter the overall equilibrium constant ($K_{\text{eq}}$) or the net standard free energy change ($\Delta G^\circ$).
- **Option-by-Option Evaluation**:
- **Option (A) [INCORRECT]**: Enzymes do not decrease the ground-state energy of the substrate; altering substrate ground-state energy would change $\Delta G^\circ$, which enzymes cannot do.
- **Option (B) [CORRECT]**: Enzymes catalyze chemical reactions by decreasing the activation energy ($\Delta G^\ddagger$) required to reach the transition state.
- **Option (C) [INCORRECT]**: Enzymes do not alter product stability or product ground-state free energy.
- **Option (D) [INCORRECT]**: Increasing the activation barrier would retard (inhibit) rather than catalyze the reaction.
**3. Final Answer / Verification Summary**:
- **Official GATE Answer Key**: **B**
- **Scoring Criteria**: +1.0 Mark (Negative marking: -0.33 marks).
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