# Explain how the structure of prokaryotic ribosomes differs from that of eukaryotic ribosomes, and outline the significance of this difference for antibiotic action.

> IB DP Biology Higher Level (2023 syllabus) — A2.2 Cell structure · Explain · 4 marks

## Mark scheme (4 marks)

1. Prokaryotic ribosomes are 70S (composed of 50S and 30S subunits), whereas eukaryotic ribosomes are 80S (composed of 60S and 40S subunits).
2. The structural difference means the ribosomal proteins and rRNA sequences differ between prokaryotes and eukaryotes.
3. Antibiotics such as streptomycin or erythromycin bind specifically to 70S ribosomal subunits, inhibiting bacterial protein synthesis.
4. Because eukaryotic (80S) ribosomes are structurally different, these antibiotics do not bind to them, so human/host cells are not harmed / selective toxicity is achieved.

## Key terms

- [antibiotic](https://www.gradenine.co.uk/glossary/antibiotic)

## Related

- [Revision notes for IB DP Biology Higher Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-structure-of-prokaryotic-06ba8415) · Published by Druglandscape Ltd.