Question at position 6 What is the role of enzymes in most biochemical reactions?To slow down the reactionTo change the type of reaction that occursTo stop the reactionTo speed up the reactionClear my selection

Question

Question at position 6 What is the role of enzymes in most biochemical reactions?To slow down the reactionTo change the type of reaction that occursTo stop the reactionTo speed up the reactionClear my selection

BlackTom AI · Accepted Answer

1. Enzymes are biological catalysts that increase the rate of biochemical reactions by lowering the activation energy (Ea) required for the reaction. Key concepts: catalyst, activation energy, active site, substrate specificity, transition-state stabilization, and that enzymes do not change the overall free energy change (ΔG) or the identity of reactants/products.

2. Step-by-step reasoning:
- Enzymes bind substrates at an active site, orienting them and stabilizing the transition state.
- Stabilizing the transition state decreases Ea, which increases the reaction rate according to the Arrhenius relationship.
- Because ΔG for the reaction is unchanged, the equilibrium position (ratio of products to reactants at equilibrium) remains the same; only the time to reach equilibrium is shortened.
- Enzymes are not consumed by the reaction and can catalyze many substrate molecules.

3. Calculation example (showing intermediate steps):
- Arrhenius-type relation: k ∝ e^(−Ea/RT). Lowering Ea increases k exponentially.
- Suppose uncatalyzed Ea = 60 kJ/mol and catalyzed Ea = 40 kJ/mol. T = 298 K, R = 8.314 J·mol−1·K−1.
- ΔEa = 20,000 J/mol. Exponent = ΔEa / (R·T) = 20,000 / (8.314 × 298) = 20,000 / 2,477.772 ≈ 8.074.
- Rate ratio k_cat / k_uncat ≈ e^(8.074) ≈ 3.2 × 10^3.
- So the enzyme can increase the rate by thousands-fold by lowering Ea.

4. Why the correct answer is correct: "To speed up the reaction" directly states the primary role of most enzymes—acting as catalysts that accelerate biochemical reactions by lowering activation energy without changing reaction type or equilibrium.

5. Why other options are incorrect:
- "To slow down the reaction": enzymes accelerate, not decelerate (though some regulators inhibit enzymes, but that’s regulation, not the enzyme’s catalytic role).
- "To change the type of reaction that occurs": enzymes do not change the chemical identity of the reaction; they facilitate the same reaction pathway (sometimes via different mechanisms) but do not convert one reaction type into another.
- "To stop the reaction": enzymes cannot halt a reaction permanently; they only affect its rate.

6. Conclusion: The correct answer is "To speed up the reaction," which matches the provided answer.

Question at position 6 What is the role of enzymes in most biochemical reactions?To slow down the reactionTo change the type of reaction that occursTo stop the reactionTo speed up the reactionClear my selection单项选择题

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