How does an increase in substrate concentration generally affect enzyme activity?

• A. It always decreases enzyme activity
• B. It increases enzyme activity until saturation
• C. It has no effect on enzyme activity
• D. It changes the enzyme's structure

Answer: (B)

An increase in substrate concentration generally leads to an increase in enzyme activity until the enzyme becomes saturated with substrate. Initially, when substrate concentration is low, there are many active sites on the enzyme available for binding. As substrate concentration rises, more substrate molecules can bind to the enzyme, resulting in an increase in the rate of reaction.

However, this increase in activity will continue only up to a certain point—the saturation point—where all the active sites on the enzyme are occupied. Once saturation is reached, adding more substrate will not lead to an increase in the rate of reaction because there are no free active sites left for additional substrate to bind. This relationship is often illustrated using the Michaelis-Menten kinetics model, which describes how reaction velocity increases with substrate concentration up to a maximum rate (Vmax) at saturation.

This explains why the assertion that it increases enzyme activity until saturation is accurate, as it reflects the typical behavior of enzymes in response to changes in substrate concentration.