What is the effect of increasing substrate concentration on enzyme activity at a constant temperature?

• A. Continually increases activity
• B. Decreases activity
• C. Increases activity until saturation point is reached
• D. Has no effect on activity

Answer: (C)

Increasing substrate concentration typically leads to an increase in enzyme activity, but this relationship only holds true up to a certain point known as the saturation point. As more substrate is added, there are more substrate molecules available to bind to the enzyme's active sites, which allows for more product to be formed. Initially, this causes an increase in the rate of the enzymatic reaction.

However, once the enzyme molecules become saturated—that is, when all available active sites are occupied by substrate—adding more substrate does not continue to increase the reaction rate. At saturation, the maximum rate of reaction, or Vmax, is reached, and the enzyme is working as fast as it can. Any additional substrate beyond this point will not increase the rate of reaction because there are no free active sites available for the substrate to bind.

Therefore, the correct understanding is that enzyme activity will increase with increasing substrate concentration until it reaches this saturation point, after which the activity levels off despite further increases in substrate concentration. This concept is central to enzyme kinetics and is often illustrated by the Michaelis-Menten model.