Question

The figure given show the conversion of substrate into product by an enzyme. In which one of the four options, the components of the reaction labeled A, B, C, D are identified correctly.

• A. $$\begin{array}{cccc}\text{A}& \text{B}& \text{C}& \text{D}\\ \text{Potential energy}& \text{Transition state}& \text{Activation energy with enzyme}& \text{Activation energy without enzyme}\end{array}$$
• B. $$\begin{array}{cccc}\text{A}& \text{B}& \text{C}& \text{D}\\ \text{Transition state}& \text{Potential energy}& \text{Activation energy without enzyme}& \text{Activation energy with enzyme}\end{array}$$
• C. $$\begin{array}{cccc}\text{A}& \text{B}& \text{C}& \text{D}\\ \text{Potential energy}& \text{Transition state}& \text{Activation energy with enzyme}& \text{Activation energy without enzyme}\end{array}$$
• D. $$\begin{array}{cccc}\text{A}& \text{B}& \text{C}& \text{D}\\ \text{Activation energy with enzyme}& \text{Transition state}& \text{Activation energy without enzyme}& \text{Potential energy}\end{array}$$

Answer 1

The correct option is B $$\begin{array}{cccc}\text{A}& \text{B}& \text{C}& \text{D}\\ \text{Transition state}& \text{Potential energy}& \text{Activation energy without enzyme}& \text{Activation energy with enzyme}\end{array}$$

According to the most widely accepted mechanism of enzyme action, the enzyme molecule binds substrate molecule to form a temporary transition state (labelled as A) which rapidly degrades into enzyme molecule and product. The transition state has higher potential energy than that of substrate (labelled as B) or product molecule. Thus, a substrate has to pass through the energy barrier in order to form the product molecule. An uncatalyzed reaction (labelled as C) has to cross a higher barrier as compared to a reaction catalysed by an enzyme (labelled as D). Thus, enzymes work by reducing the energy barrier between substrate and the product molecules.