Paper 2 · Enzymes
Why is it advantageous for different enzymes in the body, such as pepsin and trypsin, to have different optimum pH values?
AIt lets a single type of enzyme catalyse many different reactions across all the various pH environments found throughout the digestive system and body.
BIt increases the rate of reactions taking place only in environments where the pH happens to be close to neutral, around pH seven.
CIt lets each enzyme catalyse reactions efficiently in the specific pH environment of its location, such as the acidic stomach for pepsin and the alkaline small intestine for trypsin.
DIt stops enzymes from losing their shape when the temperature of the digestive tract rises above the normal core body temperature.
Explanation: Different regions of the body maintain different pH conditions; an enzyme's optimum pH matching its working location means its ionic and hydrogen bonds, and hence its active site shape, stay intact where it actually operates, e.g. pepsin at the low pH of the stomach and trypsin at the higher pH of the small intestine. This is about pH tolerance, not temperature tolerance or catalysing unrelated reactions elsewhere.
Derived from ZIMSEC Biology Paper 2, November 2004, Q7
