At a constant enzyme concentration, increasing substrate concentration eventually stops increasing the reaction rate because
Correct answer: B. all the active sites are occupied and the enzyme is saturated
- A. the substrate begins to inhibit the enzyme
- B. all the active sites are occupied and the enzyme is saturated
- C. the enzyme is denatured by the excess substrate
- D. the products are used up
Explanation
Once every active site is engaged, adding more substrate cannot raise the rate, because the enzyme is already working as fast as it can turn substrate over. This plateau is Vmax, and reaching it means the enzyme concentration, not the substrate, is now limiting. Substrate does not denature the enzyme, and products accumulate rather than run out.
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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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