Question

pepsin, a common enzyme found in the stomach, is most active at ph values between 0.5 and 2.5. it works slowly between ph values of 2.6 and 3.4. beyond a ph of about 3.5, it becomes completely inactive and does not function. which of the explanations below most accurately explains what happens to the enzyme? a the enzyme becomes denatured causing the enzyme to not be able to function as the ph increases past 3.5. b the enzymes active site contracts into the wrong shape but it will be reversed if ph is restore to the correct range. c the enzyme slows down because the ph also changes the temperature which affects the reaction rate. d the enzyme becomes inactive because it melts into a liquid when it is not at the right ph.

Explanation:

Enzymes are proteins, and when the pH goes beyond their optimal range (in this case, beyond about 3.5 for pepsin), they denature. Denaturation changes the protein's (enzyme's) three - dimensional structure. The active site (the part that binds to the substrate) is no longer in the correct shape for the enzyme to function. This is a permanent change (unlike just a temporary shape change that could be reversed).

• Option A: When an enzyme is denatured (due to extreme pH, in this case), it cannot function. Pepsin being active in a certain pH range and becoming inactive (denatured) beyond a pH of about 3.5 fits the concept of denaturation.
• Option B: If the active site just contracts (a temporary shape change), it could be reversed. But pepsin becoming completely inactive beyond a certain pH is more about denaturation (a more permanent change) rather than a reversible active - site shape change.
• Option C: The question is about pH affecting the enzyme, not pH changing temperature.
• Option D: Enzymes are proteins, not substances that melt into a liquid at the wrong pH.

Answer:

A. The enzyme becomes denatured causing the enzyme to not be able to function as the pH increases past 3.5.