Question

Consider the following pathway:

A—> B —> C —>D —> choline (an alcohol found in lipids, whose structure you need to know for the exam.)

Inside growing cells the concentrations of compounds B, C, and D are very low. If you add drug X to growing cells, then compounds B and C accumulate and growth of cells is slower than normal.

In a test tube choline binds to the enzyme that catalyzes the reaction A —> B. Choline probably ______.

		binds to the same site as A.
		binds to the same site as B.
		is a competitive inhibitor of the enzyme.
		binds to the enzyme at a different site from A and B.

Answer 1

Since the concentration of both B and C accumulates this means the reaction rate for path after formation of C is slow, that is Cholin formation is slow and Cholin's use for cell growth has been inhibited by the enzyme.But formation of B and C is not inhibitedn which means Cholin does not bind to the same site as does A or B and also Cholin is not a competitive inhibitor of the enzyme.

So answer is cholin binds to the enzyme at different site from A and B and becomes less available for cell Growth.