Question

Which of the following describes the given graph correctly?

• A. Endothermic reaction with energy A in absence of enzyme and B in the presence of an enzyme
• B. Exothermic reaction with energy A in absence of enzyme and B in the presence of an enzyme
• C. Endothermic reaction with energy A in presence of enzyme and B in the absence of an enzyme
• D. Exothermic reaction with energy A in presence of enzyme and B in the absence of an enzyme

Answer 1

The correct option is D Exothermic reaction with energy A in presence of enzyme and B in the absence of an enzyme

In enzymatically catalysed reactions, enzymes lower the amount of activation energy required to start the reaction. Activation energy is defined as the minimum amount of extra energy required by reacting molecules to get converted into the product(s).

Exothermic reactions are those that release energy, usually in the form of heat while endothermic reactions are those that require energy usually in the form of heat to proceed.

As shown in the graph, the energy of the product formed is lower than that of the substrate molecules. It means that during the course of the reaction, energy is released. Hence, the reaction represented by both the curve is that of an exothermic process. Also, we see that curve A has a peak lower than that of the curve B. This peak refers to the transition state of the substrate being converted into the product(s). The difference in the energy level of the substrate and transition state is the activation energy required to start the reaction. We observe that this difference is the least in curve A, implying that the activation energy is also reduced. Hence, it can be said that curve A represents reaction in the presence of an enzyme.