A researcher proposes a model of an enzyme-catalyzed reaction in which a reactant is converted to a product. The model is based on the idea that the reactant passes through a transition state within the enzyme-substrate complex before the reactant is converted to the product.

Which of the following statements best helps explain how the enzyme speeds up the reaction?

Question

A researcher proposes a model of an enzyme-catalyzed reaction in which a reactant is converted to a product. The model is based on the idea that the reactant passes through a transition state within the enzyme-substrate complex before the reactant is converted to the product.

Which of the following statements best helps explain how the enzyme speeds up the reaction?

BlackTom AI · Accepted Answer

Enzymes accelerate reactions by lowering the activation energy through stabilization of the transition state.

1) Relevant knowledge points and concepts
- Transition state theory: a chemical reaction proceeds through a high-energy, short-lived transition state; the activation energy (ΔG‡) is the free-energy difference between reactants and that transition state and controls the reaction rate.
- Enzyme catalysis: enzymes provide an alternative reaction pathway with a lower ΔG‡, often by preferential binding and stabilizing the transition state.
- Thermodynamics vs kinetics: enzymes change reaction rates (kinetics) but do not change the overall free-energy change (ΔG°) between reactants and products, so they do not change equilibrium constants.

2) Step-by-step reasoning
- The uncatalyzed reaction has a certain high-energy transition state and corresponding ΔG‡ that makes the rate slow.
- If an enzyme’s active site binds most strongly to the transition state, it lowers the free energy of that state relative to the free reactants.
- Lowering the transition-state free energy reduces ΔG‡ (activation energy) and, via the Arrhenius/Eyring relationship, increases the reaction rate exponentially.
- Because the enzyme affects only the energy of the transition state along the reaction coordinate, the energies of ground-state reactants and products (and thus ΔG°) remain unchanged.

3) Calculations (conceptual)
- Reaction rate ∝ e^(−ΔG‡/RT). If enzyme lowers ΔG‡ by ΔΔG‡, rate increases by factor e^(ΔΔG‡/RT). No numeric data given, so the key is the exponential sensitivity to ΔG‡.

4) Why the correct answer is correct
- “The enzyme’s active site binds to and stabilizes the transition state, which decreases the activation energy” directly describes the established mechanism: preferential transition-state binding lowers ΔG‡ and speeds the reaction.

5) Why other options are incorrect
- Option 1 (stabilizes product, increases energy released): Stabilizing product would alter product free energy but enzymes generally do not change ΔG° or the intrinsic energy released; they change rate, not thermodynamic yield. Also stabilizing product can slow turnover by product inhibition.
- Option 2 (stabilizes reactant, decreases ΔG°): Stabilizing the reactant would not decrease the free-energy change in the direction claimed and would likely raise ΔG‡ or hinder conversion; enzymes typically do not accelerate by tightly binding ground-state reactants.
- Option 4 (binds both reactant and product increasing equilibrium constant): Enzymes do not change equilibrium constants; binding both does not increase Keq and could impede catalysis.

6) Conclusion
The explanation confirms the correct answer: “The enzyme’s active site binds to and stabilizes the transition state, which decreases the activation energy of the reaction.”

类似问题

Match the following terms about enzyme catalysis with their description: 1: Transition state 2: Binding energy 3: Active site 4: Activation energy 5: Gibbs free energy

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

Which of the following statements about the impact of enzymes on chemical reactions is FALSE?

Enzymes speed up chemical reactions without being used up in the reaction.

What would be the result of an enzyme having a greater binding energy for the substrate than for the transition state?

What best describes the role of an enzyme in a reaction?

Enzymes act as biological catalysts by accelerating chemical reactions. Which is TRUE about enzyme-substrate interactions:

Which of the following statement is NOT correct about how enzymes catalyse a reaction?

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