Some antimicrobial agents demonstrate competitive inhibition, as is represented by the relationship of sulfanilamide and
options:
A) peptidoglycan
B) para-aminobenzoic acid (PABA)
C) teichoic acid
D) gyrase
E) ribosomes
The correct answer and explanation is:
The correct answer is B) para-aminobenzoic acid (PABA).
Sulfanilamide is an example of a competitive inhibitor that targets the synthesis of folic acid in bacteria. It structurally resembles para-aminobenzoic acid (PABA), a molecule that is naturally used by bacteria to synthesize folic acid. Folic acid is essential for the production of nucleic acids and amino acids, making it crucial for bacterial growth and replication. Sulfanilamide, by mimicking PABA, competes for the same binding site on the enzyme dihydropteroate synthase. This enzyme catalyzes the conversion of PABA into dihydropteroate, a precursor in the biosynthesis of folic acid.
By occupying the enzyme’s active site, sulfanilamide prevents PABA from binding and stops the bacterial cells from synthesizing folic acid. Without this key vitamin, the bacteria are unable to divide and grow, leading to their eventual death or inability to proliferate. This form of competitive inhibition is why sulfanilamide is classified as an antimetabolite, a substance that interferes with the normal metabolic processes of the organism.
The action of sulfanilamide is specific to bacteria because humans and other mammals do not synthesize folic acid; instead, they obtain it through their diet. Therefore, sulfanilamide selectively targets bacterial cells without affecting human cells, making it an effective antimicrobial agent. This mechanism of action highlights the importance of enzymes in bacterial metabolism and the potential for drugs to block essential biochemical pathways in pathogens.