Bacterial Ribosome

A bacterial ribosome is the ribosome found in prokaryotic cells, responsible for protein synthesis in bacteria. It is a 70S ribosome, composed of a small 30S subunit and a large 50S subunit. Bacterial ribosomes are smaller and structurally distinct from eukaryotic 80S ribosomes, which is why certain antibiotics can selectively target bacterial protein synthesis without affecting human cells.

• Subunits: 70S prokaryotic ribosome = 50S (large) + 30S (small) subunits. (Remember: S values aren-t additive, but these are the classic sizes for bacterial ribosomal subunits).
• Location: In bacteria (which lack a nucleus), ribosomes float free in the cytoplasm. Thousands of ribosomes may be active in a bacterial cell, often forming polysomes (multiple ribosomes translating one mRNA).
• Antibiotic targets: Many antibiotics (e.g., streptomycin, tetracycline, erythromycin) bind to 30S or 50S subunits to inhibit bacterial protein synthesis. Because eukaryotic cytoplasmic ribosomes are 80S, these drugs target bacteria more than human cells.

• Comparative structure - A question might ask: -What ribosomal difference exists between prokaryotes and eukaryotes that allows antibiotics to target bacteria-- The answer: prokaryotic 70S vs eukaryotic 80S ribosomes.
• Mechanism detail - Some exam questions describe an antibiotic-s action (e.g., blocking the peptidyl transferase or ribosomal translocation) and ask which cellular structure it affects - the answer would be the bacterial ribosome if it-s a protein synthesis inhibitor in bacteria.
• Identification - If asked to identify a -70S ribosome,- recognize it as a prokaryotic (bacterial) ribosome, typically found in bacteria (and similarly in mitochondria/chloroplasts of eukaryotes by origin).