Enzymes activity decreases at very low or high pH because:
Correct answer: B. Enzymes become denatured
- A. Substrate concentration increases
- B. Enzymes become denatured
- C. Product formation increases
- D. Temperature becomes constant
Explanation
Excess hydrogen or hydroxide ions disturb the ionic and hydrogen bonds between the side chains that hold the tertiary structure, so the active site loses its precise shape and the substrate no longer fits. A small shift is reversible, but an extreme one denatures the enzyme permanently. This is why pepsin works at about pH 2 and trypsin at about pH 8, each being inactive in the other's conditions.
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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