# Explain how the structure of the ribosome is related to its role in protein synthesis.

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

## Mark scheme (4 marks)

1. Ribosomes are composed of two subunits (large and small) that come together to hold the mRNA in position during translation.
2. Each ribosome has a small subunit that contains a site for mRNA attachment / reading of codons.
3. The large subunit contains the A, P, and E sites (tRNA binding sites) allowing tRNA carrying amino acids to be positioned correctly for peptide bond formation.
4. Ribosomes can be free in the cytoplasm or bound to the rough endoplasmic reticulum (rER), allowing proteins to be synthesised either for use within the cell or for secretion / membrane insertion respectively.

## Key terms

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

## Related

- [Revision notes for IB DP Biology Standard Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-structure-of-the-8bee8c00) · Published by Druglandscape Ltd.