Antibiotics such as streptomycin kill bacteria without seriously harming human cells because they

  • A. block transcription in the human nucleus
  • B. dissolve the plasma membrane of bacteria only
  • C. bind to 70S ribosomes and stop bacterial protein synthesis
  • D. prevent DNA replication in both cell types equally

Explanation

Human cytoplasmic ribosomes are the larger 80S type, so drugs aimed at the bacterial 70S ribosome interfere selectively with the bacterium. This selectivity is the basis of safe chemotherapy, and it is why the ribosome difference matters clinically.

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