Explain how the structure of the Golgi apparatus is related to its role in the processing and secretion of proteins.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
The Golgi apparatus is a stack of flattened, membrane‑bound cisternae, giving a series of distinct compartments.
Vesicles carrying newly synthesised proteins from the rough endoplasmic reticulum fuse with the cis face of the Golgi, delivering the proteins for processing.
As the proteins travel from the cis to the trans face, they undergo sequential chemical modifications such as glycosylation, producing the final functional form.
From the trans face secretory vesicles bud off, carrying the processed proteins to the plasma membrane for exocytosis, allowing secretion.
Vesicles carrying newly synthesised proteins from the rough endoplasmic reticulum fuse with the cis face of the Golgi, delivering the proteins for processing.
As the proteins travel from the cis to the trans face, they undergo sequential chemical modifications such as glycosylation, producing the final functional form.
From the trans face secretory vesicles bud off, carrying the processed proteins to the plasma membrane for exocytosis, allowing secretion.
Examiner tips
- Use the word ‘cis’ and ‘trans’ to show directionality; examiners reward clear sequence.
- Mention glycosylation as a key modification; it is a specific detail expected for full marks.
- Show that vesicle fusion occurs at the cis face and budding at the trans face to demonstrate structure–function link.
Common mistakes
- Confusing the cis and trans faces or omitting one of them.
- Failing to mention the role of vesicles (fusion or budding).
- Using vague terms like ‘processing’ without specifying glycosylation or other modifications.
Mark scheme (4 marks)
- The Golgi apparatus is composed of a stack of flattened membrane-bound cisternae, providing a series of compartments in which sequential modification of proteins can occur.
- Vesicles from the rough endoplasmic reticulum (rER) fuse with the cis face of the Golgi, delivering newly synthesised proteins for processing.
- As proteins move through the cisternae from cis to trans, they are chemically modified (e.g. glycosylation / addition of carbohydrate chains), producing the final functional form.
- Secretory vesicles bud off from the trans face and carry the processed proteins to the cell surface membrane for exocytosis, enabling secretion.
Related
- All IB DP Biology Standard Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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