Essential Genetics 6th Edition by Daniel Hartl

Exercise 9

Shown here is part of a metabolic pathway in a bacterium in which a substrate metabolite (small molecule) X is converted into a final product metabolite W through a sequence of three steps catalyzed by the enzymes A, B, and C. Each of the
enzymes is the product of a different gene.

Which metabolites would be expected to be missing, and which present in excess, in cells that are mutant for:
(a) Enzyme A?
(b) Enzyme B?
(c) Enzyme C?