Which type of ribosome is characteristic of bacteria and mitochondria and is a common antibiotic target?

• A. 80S
• B. 60S
• C. 70S
• D. 40S

Answer: (C)

Ribosome size and composition vary across organisms, and this difference is key for how some drugs work. Bacteria and mitochondria both use 70S ribosomes, made of a 50S large subunit and a 30S small subunit. In contrast, eukaryotic cytosolic ribosomes are 80S (40S plus 60S). Because antibiotics can specifically disrupt the 70S ribosome without as strongly affecting the 80S ribosome, many drugs that inhibit bacterial protein synthesis target the 70S type. This is why the 70S ribosome is a common antibiotic target—the same ribosome type is found in bacteria and in the mitochondria of eukaryotic cells, enabling selective interference with prokaryotic translation.