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.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
The rER is studded with ribosomes on its cytoplasmic surface, where translation of mRNA occurs, so polypeptides are synthesised directly at the membrane.
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.
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.
Vesicles bud off from the rER membrane, enclosing the processed proteins, and transport them to the Golgi apparatus for further modification and eventual secretion.
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.
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.
Vesicles bud off from the rER membrane, enclosing the processed proteins, and transport them to the Golgi apparatus for further modification and eventual secretion.
Examiner tips
- Use the word ‘studded’ or ‘covered’ to describe ribosomes on the rER surface. Mention that polypeptides are threaded into the lumen during synthesis. Highlight the large surface area and polysomes for high throughput. Show the vesicle transport step to the Golgi.
- Use concise, exam‑style sentences; avoid unnecessary words.
Mark scheme (4 marks)
- The rER is studded with ribosomes on its cytoplasmic surface, where translation of mRNA occurs, so polypeptides are synthesised directly at the membrane.
- 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.
- 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.
- 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 in this question
Related
- All IB DP Biology Standard Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
More Cell structure questions
- Explain how the structure of the nuclear envelope is related to its function in …
- Explain how the ultrastructure of a mitochondrion is related to its role in aero…
- Explain how the structure of the Golgi apparatus is related to its role in the p…
- Distinguish between prokaryotic and eukaryotic cells in terms of their internal …
- Explain how the structure of the cell surface membrane is related to its functio…
- Explain how the structure of the ribosome is related to its role in protein synt…