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 enzymes active site contracts into the wrong shape but it will be reversed if ph is restore to the correct range.
b the enzyme becomes denatured causing the enzyme to not be able to function as the ph increases past 3.5.
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 their function depends on their three - dimensional structure. When the pH is too high (beyond 3.5 for pepsin), the enzyme (pepsin) becomes denatured. Denaturation is a process where the protein's structure is disrupted. This disruption affects the enzyme's active site (the part that binds to the substrate). Once denatured, the enzyme cannot function properly.

• Option A: When an enzyme is denatured (beyond a certain pH like 3.5 for pepsin), the change is usually irreversible. So, the idea that the active - site shape change is reversible is incorrect.
• Option B: As pH increases past 3.5, pepsin is denatured. Denaturation causes the enzyme to lose its function, which aligns with the description in the problem (becomes completely inactive).
• Option C: There is no mention in the problem that pH change affects temperature. The slow - down (between pH 2.6 - 3.4) is due to sub - optimal pH for the enzyme, not a temperature change caused by pH.
• Option D: Enzymes (proteins) do not melt into a liquid when the pH is wrong. Denaturation is a structural (not a state - of - matter) change.

Answer:

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