Question

below is a metabolic pathway having 3 chemical reactions and 3 enzymes. enzyme 1 has 2 binding sites--1 for the substrate a and another for the end product d. as the pathway proceeds, the end product in higher quantities will react with enzyme 1, blocking the enzymes binding to the substrate. which statement is true about this pathway? enz1 enz2 enz3 substrate a --> b --> c --> d end product a as a result of the inhibition of the enzyme, there will eventually be less substrate converted to the end product d. b all of the choices are correct. c enzyme 1 has an active site and a regulatory site. d this is a case of noncompetitive inhibition.

Explanation:

• Option A: When enzyme 1 is inhibited (by end - product D), it cannot bind to substrate A effectively. Since enzyme 1 is the first enzyme in the pathway \(A

ightarrow B
ightarrow C
ightarrow D\), less substrate A will be converted to B, and subsequently, less B to C and less C to D. So, there will be less substrate converted to end - product D.

• Option C: Enzyme 1 has a binding site for substrate A (active site) and a binding site for end - product D (regulatory site as it regulates the enzyme's activity).
• Option D: In non - competitive inhibition, the inhibitor (here, end - product D) binds to a site other than the active site (the regulatory site in enzyme 1) and changes the enzyme's conformation so that it cannot bind to the substrate (A) effectively. This is exactly what is happening in the given pathway.

Since options A, C, and D are all correct, option B (All of the choices are correct) is the right answer.

Answer:

B. All of the choices are correct.