Which type of ribosomes are found in bacterial cells?
Prokaryotic translation machinery centers on 70S ribosome sedimenting at 70 Svedberg units, approximately 2.5 MDa particle comprising small 30S subunit containing 16S rRNA about 1542 nucleotides and 21 ribosomal proteins responsible for decoding mRNA via Shine-Dalgarno interaction pairing with anti-Shine-Dalgarno near 3 prime end of 16S, and large 50S subunit containing 23S rRNA 2900 nucleotides, 5S rRNA, and 33 proteins harboring peptidyl transferase center catalyzing peptide bond formation and exit tunnel guiding nascent chain. Initiation uses initiation factors IF1, IF2, IF3 and formyl-methionine tRNAfMet recognizing start codon, elongation factors EF-Tu and EF-G hydrolyze GTP ensuring decoding accuracy. 40S and 60S are eukaryotic cytoplasmic subunits assembling into 80S ribosome, distinct in rRNA expansion segments and protein composition including larger size. Mitochondrial and chloroplast ribosomes are 55-70S retaining bacterial ancestry, explaining antibiotic sensitivity to bacterial-specific drugs. Clinically important, aminoglycosides, tetracyclines, chloramphenicol and macrolides selectively inhibit bacterial 70S initiation and elongation without blocking cytosolic 80S, enabling selective toxicity for antimicrobial therapy.
Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 6: 70S Bacterial Ribosomes and Antibiotics.