# Explain how the structure of the rough endoplasmic reticulum (rER) is related to its role in the production and processing of proteins destined for secretion.

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

## Mark scheme (4 marks)

1. The rER is studded with ribosomes on its cytoplasmic surface, where translation of mRNA occurs, so polypeptides are synthesised directly at the membrane.
2. Newly synthesised polypeptides are threaded into the lumen of the rER as they are made, keeping them separate from the cytoplasm and allowing folding / modification to begin.
3. The extensive membrane network / large surface area of the rER provides space for multiple ribosomes (polysomes) and supports the simultaneous processing of large quantities of secretory protein.
4. Vesicles bud off from the rER membrane, enclosing the processed proteins, and transport them to the Golgi apparatus for further modification and eventual secretion.

## Key terms

- [rough endoplasmic reticulum](https://www.gradenine.co.uk/glossary/rough-endoplasmic-reticulum)

## Related

- [Revision notes for IB DP Biology Standard Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-structure-of-the-00781636) · Published by Druglandscape Ltd.