Question

The diagram illustrates energy changes in an enzyme controlled reaction. Which of the following represents the lowering of the activation energy?

• A. X
• B. Y
• C. Z
• D. Z-Y

Answer 1

The correct option is D Z-Y

For a reactant to be converted to product, it needs to pass through a compulsory high energy state called the "transition state", which is represented as the peak in the diagram.

Activation energy is the energy that is required for the substrate to reach the transition state from where it can form a product.

Z represents the activation energy required by the substrate to reach transition state without an enzyme (non-enzymatic reaction).
Y represents the activation energy required by the substrate to reach transition state with the enzyme (enzymatic reaction).

Hence, Z-Y represents the lowering of the activation energy due to presence of enzyme.
X represents the difference in free energy of the substrate and product.