Consider the biochemical pathway: A-E1?B-E2?C. If Enzyme 2 is inactive, which of the following compounds will accumulate?
Consider the biochemical pathway: A-E1?B-E2?C
If Enzyme 2 is inactive, which of the following compounds will accumulate?
The Correct Answer and Explanation is:
Correct Answer: B
Explanation:
In biochemical pathways, compounds are converted from one form to another through enzymatic reactions, each step being catalyzed by a specific enzyme. Let’s break down the given pathway:
A --(E1)--> B --(E2)--> C- E1 (Enzyme 1) catalyzes the conversion of A to B.
- E2 (Enzyme 2) catalyzes the conversion of B to C.
Now, the question states that Enzyme 2 is inactive. This means that E2 is not functioning, and therefore, it cannot convert B into C. However, Enzyme 1 is still active, so it will continue to convert A into B.
Because B cannot be processed further into C, B will accumulate over time. This is a common principle in metabolic biochemistry where a block at a certain enzymatic step leads to a buildup of the substrate for that reaction.
Let’s consider the roles of each compound:
- A: The starting molecule; it is converted to B by E1.
- B: The intermediate product; it accumulates because E2 is inactive.
- C: The final product; its synthesis is blocked because E2 is inactive.
This type of pathway regulation is not only theoretical but has practical implications. In inborn errors of metabolism, for example, a genetic defect in an enzyme leads to accumulation of a substrate, which can be toxic or interfere with other processes. For example, in phenylketonuria (PKU), a deficiency in the enzyme that converts phenylalanine to tyrosine leads to the accumulation of phenylalanine.
In summary, when an enzyme in a biochemical pathway is nonfunctional, the compound just before the block accumulates, because it is produced by the preceding step but cannot proceed further. Therefore, the correct answer is B, as it is the substrate for the inactive enzyme (E2).