Which antibiotic class inhibits folic acid synthesis by acting as PABA analogs?

• A. Nucleic Acid Synthesis
• B. Protein Synthesis
• C. Folic Acid Synthesis
• D. Metabolic Pathways

Answer: (C)

PABA analogs inhibit folic acid synthesis by competing with para-aminobenzoic acid for the enzyme dihydropteroate synthase in the bacterial folate pathway. When these antibiotics bind the enzyme, the normal incorporation of PABA into dihydropteroate is blocked, preventing the production of dihydrofolate and, downstream, tetrahydrofolate. Without folate derivatives, bacteria can’t synthesize thymidine and purines needed for DNA replication, so growth slows or stops. Humans don’t rely on bacterial folate synthesis because we obtain folate from our diet, which explains the selective toxicity of these drugs. So the described action—inhibiting folic acid synthesis by acting as PABA analogs—fits the class that targets this pathway.