# DBT JRF 2020 — Question 21

Exam: DBT JRF 2020 · Section: A · Topic: Biochemistry · Difficulty: Easy

## Question

In enzyme kinetics, if the enzyme concentration is doubled

## Options

- **A.** $K_m$ becomes half
- **B.** $K_m$ does not change
- **C.** $K_m$ increases 4-fold
- **D.** $K_m$ becomes double

## Answer

Option B

## Explanation

The Michaelis constant $K_m$ is defined as the substrate concentration at which reaction velocity equals $\dfrac{V_{\max}}{2}$ : $v = \dfrac{V_{\max}[S]}{K_m + [S]}$ . $K_m$ is an intrinsic property of the enzyme–substrate pair, reflecting binding affinity and catalytic rate constants ( $K_m = \dfrac{k_{-1} + k_{cat}}{k_1}$ ). It is completely independent of enzyme concentration. When enzyme concentration is doubled, $V_{\max}$ doubles (since $V_{\max} = k_{cat}[E_T]$ ), but $K_m$ remains unchanged because the ratio of rate constants does not change.

Source: https://mypyqbuddy.com/questions/in-enzyme-kinetics-if-the-enzyme-concentration-is-6a05a8a02adafec4702931fb