Final answer:
Sulfa drugs interfere with bacterial nucleic acid synthesis by inhibiting folic acid biosynthesis, which is critical for the production of components necessary for DNA and RNA.
Step-by-step explanation:
The sulfa drugs affect bacteria by interfering with folic acid synthesis. Specifically, they inhibit the enzyme responsible for producing dihydrofolic acid. This blockage prevents the biosynthesis of folic acid and subsequently blocks the synthesis of pyrimidines and purines, which are essential components for nucleic acid synthesis. Since humans acquire folic acid through their diet and do not synthesize it internally, sulfa drugs are selectively toxic to bacteria and do not affect human cells in the same way, making them effective antibiotics.