# Explain how the endomembrane system enables a secretory protein to be correctly processed and exported from a eukaryotic cell.

> IB DP Biology Higher Level (2023 syllabus) — B2.2 Organelles and compartmentalisation · Explain · 4 marks

## Mark scheme (4 marks)

1. Ribosomes on the rough endoplasmic reticulum (RER) synthesise the protein directly into the lumen of the RER.
2. The protein undergoes initial folding and post-translational modification (e.g., glycosylation) within the RER lumen.
3. The protein is packaged into transport vesicles that bud from the RER and fuse with the Golgi apparatus.
4. Further modification and sorting occur in the Golgi apparatus; secretory vesicles bud from the trans face and fuse with the plasma membrane, releasing the protein by exocytosis.

## Key terms

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

## Related

- [Revision notes for IB DP Biology Higher Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-endomembrane-system-enables-c7952507) · Published by Druglandscape Ltd.