Question

Given below are two statements: Assertion (A): Allosteric enzyme do not usually show classical Michaelis-Menten kinetic relationships between substrate concentration and \(K_m\). Reason (R): Their kinetic behaviour is greatly altered by variations in concentration of allosteric modulator.

• A. Both (A) and (R) are correct and (R) is the correct explanation of (A)
• B. Both (A) and (R) are correct but (R) is not the correct explanation of (A)
• C. (A) is correct but (R) is not correct
• D. (A) is not correct but (R) is correct

Hint:

Allosteric enzymes usually show sigmoidal kinetics instead of classical Michaelis-Menten hyperbolic kinetics because of cooperativity and allosteric regulation.

Answer 1

The Correct Option is A

Concept:
Allosteric enzymes are enzymes whose activity is controlled by molecules binding at sites other than the active site. These regulatory molecules are called allosteric modulators.

Step 1: Check Assertion (A).
Classical Michaelis-Menten enzymes usually show a hyperbolic curve between reaction velocity and substrate concentration. But allosteric enzymes usually show sigmoidal kinetics because their subunits show cooperative behavior. \[ A \text{ is correct} \]

Step 2: Check Reason (R).
Allosteric modulators can either activate or inhibit the enzyme. When the concentration of allosteric modulator changes, the enzyme activity changes significantly. \[ R \text{ is correct} \]

Step 3: Check explanation.
Allosteric enzymes do not follow classical Michaelis-Menten kinetics because their behavior is affected by allosteric modulators and cooperativity. Therefore, Reason correctly explains the Assertion. \[ \therefore \text{Correct Answer is (A)} \]