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? a the enzymes active site binds to and stabilizes the reactant, which decreases the free - energy change of the reaction. b the enzymes active site binds to and stabilizes the transition state, which decreases the activation energy of the reaction. c the enzymes active site binds to and stabilizes the product, which increases the amount of energy released by the reaction. d the enzymes active site binds to and stabilizes both the reactant and the product at the same time, which increases the reactions equilibrium constant.

Explanation:

Enzymes speed up reactions by lowering activation energy ($E_a$), the energy needed to reach the transition state. Stabilizing the transition state reduces $E_a$, allowing more reactants to overcome this barrier and react faster. Option A is wrong because enzymes don’t change the free-energy change ($\Delta G$) of the reaction. Option C is incorrect as stabilizing products doesn’t increase energy release (which is fixed by $\Delta G$). Option D is false because enzymes don’t alter the equilibrium constant; they only speed up reaching equilibrium. Thus, B is the correct explanation.

Answer:

B. The enzyme’s active site binds to and stabilizes the transition state, which decreases the activation energy of the reaction.