What is the mechanism of action of sulfonamides?

The mechanism of action of sulfonamides revolves around their ability to compete with para-aminobenzoic acid (PABA) in the bacterial folate synthesis pathway. Sulfonamides are structural analogs of PABA, which is a key substrate required for the synthesis of folate by many bacteria. By binding to the active site of the enzyme dihydropteroate synthase, sulfonamides effectively inhibit the conversion of PABA to dihydropteroic acid, a crucial step in folate biosynthesis.

Folate is essential for bacterial growth and reproduction as it is required for DNA synthesis and repair. By disrupting this process, sulfonamides prevent the growth of bacteria, making them effective antimicrobial agents.

In contrast, the other options describe mechanisms that are typical of different classes of antibiotics. Inhibition of DNA replication is associated with certain antibiotics like fluoroquinolones. Protein synthesis inhibitors include tetracyclines and aminoglycosides, while drugs that block cell wall synthesis include beta-lactams and vancomycin. Each of these mechanisms targets different pathways vital for bacterial survival, but sulfonamides specifically act through the competitive inhibition of folate synthesis via PABA.