Biochemistry · Enzyme
Ribosome (and the antibiotics that target it) !
The ribosome is the protein factory: it reads mRNA and joins amino acids. Bacterial ribosomes differ from human ones, so many antibiotics target them.
Updated 2026-11-01
Key facts
- Human 80S = 60S (28S, 5.8S, 5S rRNA + about 47 proteins) + 40S (18S rRNA + about 33 proteins).
- Bacterial 70S = 50S (23S and 5S rRNA) + 30S (16S rRNA). Mitochondrial: 55S, similar to bacterial.
- Peptidyl transferase is the large-subunit rRNA: the ribosome is a ribozyme.
- Three tRNA sites: A (the aminoacyl-tRNA arrives), P (holds the chain), E (exit).
- Antibiotics on the 30S: aminoglycosides, tetracyclines. On the 50S: macrolides, chloramphenicol, clindamycin, linezolid, streptogramins.
- Also called
- 80S ribosome, 70S ribosome
- EC number
- 2.3.2.12
- Genes
- RPL/RPS genes; RNA45SN (28S, 18S, 5.8S rRNA); RNA5S
Regulation
- Assembly happens in the nucleolus; ribosome numbers follow growth signals (mTOR).
- eIF2α phosphorylation (stress, viral infection, amino acid shortage) slows initiation across the cell.
- mTORC1 boosts translation of ribosomal-protein mRNAs (5' TOP sequences).
Inhibitors and toxins
- Aminoglycosides (30S: misreading of the code)
- Tetracyclines (30S: block A-site entry)
- Macrolides (50S: plug the peptide exit tunnel)
- Chloramphenicol, linezolid, clindamycin (50S, peptidyl transferase centre)
- Homoharringtonine / omacetaxine and cycloheximide (eukaryotic 80S)
Clinical notes
- Some antibiotics affect the mitochondrial ribosome (bacteria-like): aminoglycoside ototoxicity (12S rRNA variant m.1555A>G) and chloramphenicol myelosuppression.
- 'Ribosomopathies' such as Diamond-Blackfan anaemia (RPS/RPL proteins) cause red-cell failure.
- Homoharringtonine (omacetaxine) is used in resistant chronic myeloid leukaemia; it occupies the 60S A site.
Related conditions
- Community-acquired pneumonia
- Tuberculosis
- MELAS (mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes)
Related
- Translation and the genetic code
- Transfer RNA (tRNA)
- RNA polymerases I, II and III
- Central dogma of molecular biology
Test yourself
Think of the answer, then tap the question to see it.
Which subunits make up the human and the bacterial ribosome?
Human 80S = 60S + 40S; bacterial 70S = 50S + 30S.
Why can aminoglycosides cause deafness?
The mitochondrial ribosome resembles the bacterial one; certain 12S rRNA variants make it more sensitive to these drugs.
Which antibiotics act on the 30S subunit?
Aminoglycosides and tetracyclines.
Which drug binds the peptidyl transferase centre of the human ribosome in structure 6QZP?
Homoharringtonine (HMT), bound at the peptidyl transferase centre of the human 60S subunit.
Educational information, not medical advice. For any symptom, see a health professional.
Sources: RPL3: Large ribosomal subunit protein uL3 (human) (UniProt, 2026); 6QZP: High-resolution cryo-EM structure of the human 80S ribosome (RCSB Protein Data Bank, 2026); Translation (Reactome, 2026); Ribosome (National Human Genome Research Institute (NHGRI), 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).
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Representative model, for educational purposes only.