What do sulfa drugs competitively inhibit in bacteria?

Sulfa drugs are a class of antibiotics that specifically target the bacterial synthesis of folic acid, an essential component for DNA and RNA synthesis. The correct answer involves the competitive inhibition of dihydrofolic acid production, which is an intermediate in the folate biosynthesis pathway.

Bacteria require folate to synthesize nucleic acids and ultimately to grow and divide. Sulfa drugs mimic para-aminobenzoic acid (PABA), a substrate used by bacteria to produce dihydrofolate. By competitively inhibiting the enzyme that catalyzes this reaction, sulfa drugs effectively reduce the production of dihydrofolic acid, leading to a depletion of folate levels in bacteria and ultimately hindering their growth.

This mechanism makes sulfa drugs particularly effective as they specifically target bacterial processes without affecting human cells, which do not synthesize folate and instead obtain it through diet. Understanding this mechanism of action is crucial for appreciating how sulfa drugs function therapeutically and their role in treating bacterial infections.