# Explain the role of ribosomes in ensuring the accuracy of translation during protein synthesis.

> IB DP Biology Higher Level (2023 syllabus) — D1.2 Protein synthesis · Explain · 4 marks

## Mark scheme (4 marks)

1. Ribosomes have two subunits (small and large) that come together at the start codon on the mRNA, positioning the mRNA correctly for reading.
2. The small subunit contains the decoding centre / A site region where the mRNA codon is read, ensuring the correct codon–anticodon pairing occurs.
3. The large subunit contains the peptidyl transferase centre (PTC), a ribozyme activity in the 23S/28S rRNA, which catalyses peptide bond formation between adjacent amino acids.
4. The ribosome moves along the mRNA in the 5′ to 3′ direction (translocation), shifting by one codon at a time, so that each codon is read sequentially and in the correct reading frame.

## Key terms

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

## 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-the-role-of-ribosomes-in-62aebde9) · Published by Druglandscape Ltd.