Which statement correctly pairs a drug with its primary enzymatic target in folate synthesis?

Which statement correctly pairs a drug with its primary enzymatic target in folate synthesis?

• A. Sulfonamides target dihydropteroate synthase.
• B. Sulfonamides target dihydrofolate reductase.
• C. Sulfonamides target thymidylate synthase.
• D. Sulfonamides target dihydrofolate synthase.

Answer: (A)

Sulfonamides work by blocking the bacterial enzyme dihydropteroate synthase, which is the first step in folate synthesis. They are structural analogs of PABA and compete with it for this enzyme, preventing the formation of dihydropteroic acid and downstream folate compounds needed for making DNA precursors. Because humans do not synthesize folate de novo and lack this enzyme, sulfonamides selectively disrupt bacterial growth. The other enzymes mentioned are targeted by different drugs: dihydrofolate reductase is inhibited by trimethoprim, which is often used in combination with sulfonamides for a stronger effect; thymidylate synthase inhibition is a mechanism of certain anticancer drugs like 5-fluorouracil; and dihydrofolate synthase is not the usual target in this bacterial pathway.

Sulfonamides work by blocking the bacterial enzyme dihydropteroate synthase, which is the first step in folate synthesis. They are structural analogs of PABA and compete with it for this enzyme, preventing the formation of dihydropteroic acid and downstream folate compounds needed for making DNA precursors. Because humans do not synthesize folate de novo and lack this enzyme, sulfonamides selectively disrupt bacterial growth.

The other enzymes mentioned are targeted by different drugs: dihydrofolate reductase is inhibited by trimethoprim, which is often used in combination with sulfonamides for a stronger effect; thymidylate synthase inhibition is a mechanism of certain anticancer drugs like 5-fluorouracil; and dihydrofolate synthase is not the usual target in this bacterial pathway.