Final answer:
Sulfonamides act as competitive inhibitors of the enzyme involved in bacterial folic acid synthesis, inhibiting growth of bacteria while being selectively toxic due to the difference in folic acid metabolism between humans and bacteria.
Step-by-step explanation:
Sulfonamides are synthetic antibiotics that function by inhibiting bacterial folic acid synthesis.
They are competitive antagonists of para-aminobenzoic acid (PABA), which bacteria utilize to synthesize folic acid. Specifically, sulfonamides inhibit sulfihydropteroate synthase, the enzyme crucial for the conversion of PABA into dihydrofolic acid, the immediate precursor of folic acid.
This blockade impairs the synthesis of purines and pyrimidines necessary for bacterial nucleic acid formation, thereby providing a bacteriostatic action against various pathogens.
As humans acquire folic acid through diet rather than synthesizing it, sulfonamides selectively target bacteria, although allergic reactions are relatively common in some individuals.