Question

The figure given shows the conversion of a substrate into product by an enzyme. Which one of the four options of reaction labelled as A, B, C and D are identified correctly?

• A. A- Potential energy, B- Transition state, C- Activation energy with enzyme, D- Activation energy without enzyme
• B. A- Transition state, B- Potential energy, C- Activation energy without enzyme, D- Activation energy with enzyme
• C. A- Potential energy, B- Transition state, C- Activation energy without enzyme, D- Activation energy with enzyme
• D. A- Activation energy, B- Transition state, C- Activation energy without enzyme, D- Potential energy with enzyme

Answer 1

The correct option is B A- Transition state, B- Potential energy, C- Activation energy without enzyme, D- Activation energy with enzyme

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

So, the correct answer is 'A- Transition state, B- Potential energy, C- Activation energy without enzyme, D- Activation energy with enzyme'