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. Why does this happen?
A)
The enzyme inactivates because it melts into a liquid when it is not at the right pH.
B)
The protein chain in the enzyme is denatured, permanently inactivating it as the pH approaches 7.
C)
The enzymes slow down, because changing the pH changes the temperature as well, and affects the reaction.
D)
The enzyme's active site contracts into the wrong shape, but this is always reversible if the right pH is restored.

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. Why does this happen?
A)
The enzyme inactivates because it melts into a liquid when it is not at the right pH.	
B)
The protein chain in the enzyme is denatured, permanently inactivating it as the pH approaches 7.	
C)
The enzymes slow down, because changing the pH changes the temperature as well, and affects the reaction.	
D)
The enzyme's active site contracts into the wrong shape, but this is always reversible if the right pH is restored.

anonymous · Answer

D is the right answer.

A is wrong because nothing 'melts' when pH changes. some things can become soluble, yes, but melting is definitely not right.

B is wrong because of the word 'permanently'. enzyme denaturing because of pH is reversible most of the time. with pepsin, it definitely is.

C is just dumb. :-) pH changes and temperature changes are two wholely separate things.