Question

In an enzymatic reaction, when will the substrate concentration be equal to the Michaelis constant, Km?

• A. When the velocity of the reaction is halved
• B. When the velocity of the reaction is doubled
• C. When the velocity of the reaction is half the maximum velocity
• D. When the substrate concentration is doubled

Answer 1

The correct option is C

When the velocity of the reaction is half the maximum velocity

In an enzymatic reaction, the rate of the reaction increases as we increase the substrate concentration, till a point where the reaction reaches the maximum velocity Vmax. Once this upper limit has been attained, further increase in substrate concentration will not increase the rate of the reaction, as all the substrate binding sites on the enzyme will be saturated. The substrate concentration at half the maximum velocity is defined as the Michaelis constant, Km.