In zero-order kinetics, increasing substrate concentration has what effect on the rate?

In zero-order kinetics, increasing substrate concentration has what effect on the rate?

• A. No effect on the rate
• B. Rate increases linearly
• C. Rate depends on substrate concentration
• D. Rate is independent of enzyme concentration

Answer: (A)

At high substrate concentrations the enzyme becomes saturated, so every active site is busy and the reaction proceeds at its maximum velocity. In this saturated state the rate is fixed by the enzyme’s turnover number and amount, not by how much substrate is present. So increasing substrate concentration cannot push the rate higher; it plateaus at Vmax. If you change the enzyme quantity, Vmax would shift accordingly, but once saturation is reached, substrate amount no longer controls the rate. This is the essence of zero-order kinetics with respect to substrate: the rate is independent of substrate concentration.

At high substrate concentrations the enzyme becomes saturated, so every active site is busy and the reaction proceeds at its maximum velocity. In this saturated state the rate is fixed by the enzyme’s turnover number and amount, not by how much substrate is present. So increasing substrate concentration cannot push the rate higher; it plateaus at Vmax. If you change the enzyme quantity, Vmax would shift accordingly, but once saturation is reached, substrate amount no longer controls the rate. This is the essence of zero-order kinetics with respect to substrate: the rate is independent of substrate concentration.