Question

cooperativity is a form of allosteric activation in which ...

the product of a metabolic pathway serves as a competitive inhibitor of an early enzyme in the pathway.
all of the enzymes in a metabolic pathway are contained within a single multienzyme complex.
completion of one step in a metabolic pathway is required before a subsequent step can occur.
binding of a substrate molecule to one active site in a multisubunit enzyme stimulates the binding of substrate molecules to the active sites of other subunits.

Explanation:

To solve this, we analyze each option:

• Option 1: Describes feedback inhibition (product inhibition), not cooperativity.
• Option 2: Describes a multienzyme complex, not cooperativity.
• Option 3: Describes sequential reactions in a pathway, not cooperativity.
• Option 4: Cooperativity in allosteric enzymes (multisubunit) involves one substrate binding enhancing others' binding to subunits. This matches the definition of cooperativity.

Answer:

D. binding of a substrate molecule to one active site in a multisubunit enzyme stimulates the binding of substrate molecules to the active sites of other subunits.