Question

Which of the following statements is relevant in explaining why sulfonamides are effective?

1) Sulfonamides attach to sterol lipids in the pathogen, disrupt the membranes, and lyse the cells
2) Sulfonamides prevent the incorporation of amino acids into the polypeptide chains
3) Humans and microbes use folic acid and PABA differently in their metabolism
4) Sulfonamides inhibit DNA replication in both pathogens and human cells

Answer 1

Sulfonamides are effective because they inhibit bacterial folic acid synthesis competitively, without affecting human cells due to selective toxicity, resulting in a bacteriostatic effect on pathogen growth.

Step-by-step explanation:

Sulfonamides are effective because they selectively inhibit the synthesis of folic acid in bacteria by being competitive antagonists to para-aminobenzoic acid (PABA).

This is because sulfonamides, being structural analogs of PABA, compete with it for the active site of the enzyme involved in the production of dihydrofolic acid.

Since bacteria must synthesize their own folic acid and cannot utilize preformed folic acid, while humans obtain folic acid from their diet, this mode of action represents selective toxicity, allowing sulfonamides to target bacteria without impacting human cells.

Thus, the most relevant statement in explaining the effectiveness of sulfonamides is: Humans and microbes use folic acid and PABA differently in their metabolism.

Allergic reactions to sulfa drugs are common, and the deficiency of folic acid in microbes due to sulfonamide action can lead to poor synthesis of pyrimidine and thus affect DNA synthesis and cell division, providing a bacteriostatic effect against a wide array of pathogens.