Q.29 The order n for a given substrate concentration in an enzyme catalyzed reaction following
Michaelis-Menten kinetics, is
(A) n = 1 (B) n = 0 (C) n is not defined (D) 0 ≤ n ≤ 1
Michaelis-Menten Enzyme Order: Reaction Kinetics Explained
Michaelis-Menten kinetics shows mixed-order behavior where the reaction order n with respect to substrate varies from 0 to 1 depending on concentration. For a given substrate concentration, the order is not fixed at a single value, making option (D) 0 ≤ n ≤ 1 correct.
Reaction Order Concept
In enzyme kinetics, order n describes how velocity v depends on substrate [S]: first-order means v ∝ [S] (n=1), zero-order means v independent of [S] (n=0).
Michaelis-Menten equation v=Vmax[S]/Km+[S] yields mixed order overall.
At any specific [S], n falls between these limits, calculated as n=[S]Km+2[S].
Correct Answer Breakdown
Option (D) 0 ≤ n ≤ 1 captures the reality: n transitions continuously with [S].
When [S] << Km, v≈Vmax/Km[S] so n=1 (first-order).
When [S] >> Km, v ≈ V_max so n=0 (zero-order).
Options Analysis Table
| Option | Value | Why Correct/Incorrect |
|---|---|---|
| (A) n = 1 | Always first-order | True only at low [S] << Km; fails at saturation. |
| (B) n = 0 | Always zero-order | True only at high [S] >> Km; ignores unsaturated case. |
| (C) n not defined | No order possible | Incorrect; fractional orders are well-defined mathematically. |
| (D) 0 ≤ n ≤ 1 | Varies between limits | Matches full kinetic profile for any given [S]. |
Exam Application
This tests understanding of non-integer kinetics in biochemistry exams like NEET, distinguishing Michaelis-Menten from simple orders.
Lineweaver-Burk plots visualize the transition, aiding Km determination.
