What step in the folic acid synthesis process do sulfonamides and PAS block?

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Multiple Choice

What step in the folic acid synthesis process do sulfonamides and PAS block?

Explanation:
The drugs block the first committed step in bacterial folate synthesis, stopping the formation of dihydropteroic acid from pteridine pyrophosphate. They are structural mimics of PABA and competitively inhibit the enzyme dihydropteroate synthase, which normally catalyzes the condensation of pteridine pyrophosphate with PABA to form dihydropteroate. Without dihydropteroate, downstream production of dihydrofolate and tetrahydrofolate cannot occur, impairing synthesis of thymidine and purines needed for DNA replication. Humans don't synthesize folate de novo, so this pathway is present only in microbes, providing selective toxicity.

The drugs block the first committed step in bacterial folate synthesis, stopping the formation of dihydropteroic acid from pteridine pyrophosphate. They are structural mimics of PABA and competitively inhibit the enzyme dihydropteroate synthase, which normally catalyzes the condensation of pteridine pyrophosphate with PABA to form dihydropteroate. Without dihydropteroate, downstream production of dihydrofolate and tetrahydrofolate cannot occur, impairing synthesis of thymidine and purines needed for DNA replication. Humans don't synthesize folate de novo, so this pathway is present only in microbes, providing selective toxicity.

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