Consider the biochemical pathway: A + E1 –> B + E2 –> C (Note that A, B, and C are molecules in the pathway, E1 is enzyme 1, and E2 is enzyme 2.) If enzyme 2 is inactive, which of the following compounds will accumulate?
Multiple Choice
A only
B and C
A and B
C only
The Correct Answer and Explanation is:
Correct Answer: A and B
Explanation:
The given biochemical pathway is:
A + E1 → B + E2 → C
Let’s break this down step-by-step:
- Step 1: A is converted into B
This reaction is catalyzed by enzyme E1. If E1 is active, it will convert molecule A into molecule B. - Step 2: B is converted into C
This reaction is catalyzed by enzyme E2. If E2 is inactive, B cannot be converted into C.
What Happens When E2 is Inactive?
- Since E1 is still active, the reaction A → B continues to occur.
- However, because E2 is inactive, the reaction B → C cannot proceed.
- As a result:
- A will continue to be used and converted into B, until B accumulates to a point that feedback mechanisms (if any exist) slow down or stop E1.
- B will accumulate because it cannot be processed further into C.
- C will not be produced due to the inactivity of enzyme E2.
Thus, both A and B will be present in higher-than-expected concentrations:
- A may start to accumulate if B accumulation causes product inhibition on E1 (a common biochemical regulation).
- But more importantly, B will definitely accumulate due to the direct blockage of its conversion to C.
Why Not the Other Choices?
- A only: Incorrect because B will also accumulate.
- B and C: Incorrect. C won’t be made since E2 is inactive.
- C only: Incorrect. C cannot be formed without E2.
Conclusion:
When enzyme E2 is inactive, the pathway is blocked at the B → C step. Therefore, both A and B accumulate because:
- A continues to be used and may accumulate if E1 slows down,
- B cannot be converted and directly builds up.
Correct Answer: A and B.