Which feature is unique to bacteria and commonly targeted by antibiotics to minimize harm to human cells?

• A. Folic acid synthesis
• B. Nuclear envelope
• C. 70S ribosomes
• D. Mitochondria

Answer: (A)

The key idea is selective toxicity from a metabolic pathway that bacteria alone carry out. Bacteria must make folic acid on their own to build nucleotides, while human cells don’t synthesize folate and instead obtain it from diet. Because of this difference, antibiotics that block folate synthesis—such as those inhibiting enzymes like dihydropteroate synthase or dihydrofolate reductase—disrupt DNA and RNA production in bacteria but have relatively little direct effect on human cells. That makes folic acid synthesis a classic antibiotic target with low human toxicity.

Other features aren’t unique to bacteria in a way that offers the same safe target. The nuclear envelope is a feature of eukaryotic cells, not bacteria. While bacteria have 70S ribosomes, so do human mitochondria, and our cytoplasmic ribosomes are 80S, so targeting 70S ribosomes isn’t exclusively bacterial. Mitochondria are organelles within human cells, not present in bacteria, so that feature isn’t a bacterial hallmark either.