A change in pH away from the optimum reduces enzyme activity because it
Correct answer: B. alters the charges on the R groups, changing the shape of the active site
- A. reduces the number of substrate molecules present
- B. alters the charges on the R groups, changing the shape of the active site
- C. lowers the temperature of the mixture
- D. converts the enzyme into a substrate
Explanation
Excess hydrogen or hydroxide ions interfere with the ionic and hydrogen bonds between the side chains that hold the tertiary structure, so the active site distorts 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 pH 2 and trypsin at pH 8 and neither is active in the other's conditions.
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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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