Effect of increased substrate concentration on enzyme activity:
Correct answer: B. Increase the reaction rate until all active sites are saturated
- A. Decrease the rate of reaction
- B. Increase the reaction rate until all active sites are saturated
- C. Have no effect on the reaction rate
- D. Increase the rate of reaction in a straight diagonal line
Explanation
Rate rises steeply at first because more collisions occur between substrate and free active sites, then levels off at Vmax once every site is occupied and the enzyme is working as fast as it can. The curve is therefore hyperbolic rather than a straight line, which is what the fourth option gets wrong. Beyond saturation the enzyme concentration rather than the substrate is limiting.
This question appeared on the UHS MDCAT 2025 paper, which you can sit online with every answer explained.
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About Factors Affecting Enzyme Action
Enzyme activity changes with temperature, pH, substrate concentration and enzyme concentration because these factors affect molecular collisions and the active site. Questions also examine optimum conditions, denaturation and inhibition, while distinguishing a fall in activity caused by unsuitable conditions from permanent enzyme damage.
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