Explain how the structure of the nuclear envelope is related to its function in regulating communication between the nucleus and the cytoplasm.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
The nuclear envelope is a double‐membrane structure made of two phospholipid bilayers – an outer and an inner membrane – which isolates the DNA from the cytoplasm.
Nuclear pores are protein‑lined channels that penetrate both membranes and provide selective transport routes for molecules.
Through these pores, mRNA and ribosomal subunits are exported into the cytoplasm, allowing the products of gene expression to function outside the nucleus.
The outer membrane is continuous with the rough endoplasmic reticulum, so proteins that are synthesised on ribosomes attached to the outer membrane can be transferred directly into the ER lumen for further processing.
Nuclear pores are protein‑lined channels that penetrate both membranes and provide selective transport routes for molecules.
Through these pores, mRNA and ribosomal subunits are exported into the cytoplasm, allowing the products of gene expression to function outside the nucleus.
The outer membrane is continuous with the rough endoplasmic reticulum, so proteins that are synthesised on ribosomes attached to the outer membrane can be transferred directly into the ER lumen for further processing.
Examiner tips
- Mention the double‑membrane isolation first, then the pores, then export of mRNA/ribosomes, and finally the ER continuity.
- Use the exact terms ‘phospholipid bilayer’, ‘nuclear pores’, ‘selective transport’, ‘mRNA’, ‘ribosomal subunits’, and ‘rough endoplasmic reticulum’.
- Keep each point concise – 1–2 sentences per point.
Mark scheme (4 marks)
- The nuclear envelope consists of two phospholipid bilayers (outer and inner membranes), forming a double membrane that isolates the genetic material from the cytoplasm.
- Nuclear pores are protein-lined channels that span the double membrane and allow selective transport of molecules between the nucleus and cytoplasm.
- mRNA and ribosomal subunits are exported through nuclear pores to the cytoplasm, enabling gene expression to occur outside the nucleus.
- The outer membrane of the nuclear envelope is continuous with the rough endoplasmic reticulum, allowing direct transfer of newly synthesised proteins into the ER lumen for processing.
Key terms in this question
Related
- All IB DP Biology Higher Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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