Activation energy in enzyme reaction profiles

Steps:

• Recall that activation energy (Ea) is the minimum energy required for reactants to reach the transition state in a reaction.
• Examine the graph's energy diagram, which plots potential energy against reaction progress for enzyme-catalyzed reactions.
• Identify the region from reactant energy level to the peak (transition state) as Ea, shown as an upward arrow or shaded area.
• Compare choices: A, C, D likely represent other features like delta H or product levels, while B matches the Ea barrier.

Why B is correct:

• B corresponds to the energy difference between reactants and transition state, defining Ea per transition state theory.

Why the others are wrong:

• A: Represents the overall energy change (ΔH), not the activation barrier.
• C: Shows the energy of products, irrelevant to activation.
• D: Indicates the reverse reaction's Ea, not the forward enzyme-catalyzed path.

Final answer: B