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[Biochemistry](https://durgical.com/en/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](https://www.enzyme-database.org/query.php?ec=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](https://durgical.com/en/conditions/community-acquired-pneumonia/)
- [Tuberculosis](https://durgical.com/en/conditions/tuberculosis/)
- [MELAS (mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes)](https://durgical.com/en/conditions/melas/)

## Related

- [Translation and the genetic code](https://durgical.com/en/biochemistry/topics/translation-and-the-genetic-code/)
- [Transfer RNA (tRNA)](https://durgical.com/en/biochemistry/topics/transfer-rna/)
- [RNA polymerases I, II and III](https://durgical.com/en/biochemistry/enzymes/rna-polymerases-i-ii-and-iii/)
- [Central dogma of molecular biology](https://durgical.com/en/biochemistry/topics/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.

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Educational information, not medical advice. For any symptom, see a health professional.

Sources: [RPL3: Large ribosomal subunit protein uL3 (human)](https://www.uniprot.org/uniprotkb/P39023/entry) (UniProt, 2026); [6QZP: High-resolution cryo-EM structure of the human 80S ribosome](https://www.rcsb.org/structure/6QZP) (RCSB Protein Data Bank, 2026); [Translation](https://reactome.org/PathwayBrowser/#/R-HSA-72766) (Reactome, 2026); [Ribosome](https://www.genome.gov/genetics-glossary/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.

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