# Explain how the structural features of the nucleus enable it to regulate gene expression whilst maintaining the integrity of DNA.

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

## Mark scheme (4 marks)

1. The nuclear envelope (double membrane) physically separates DNA from the cytoplasm, protecting it from cytoplasmic enzymes/ribosomes that could damage it.
2. Nuclear pores allow selective transport of mRNA (and other molecules) out of the nucleus into the cytoplasm, enabling regulation of which gene products reach the cytoplasm.
3. DNA is associated with histone proteins forming chromatin/nucleosomes, allowing compaction and enabling gene expression to be regulated by condensing/relaxing chromatin (heterochromatin vs euchromatin).
4. The nucleolus is a specialised region within the nucleus where rRNA is synthesised and ribosomal subunits are assembled, allowing the cell to regulate the rate of protein synthesis by controlling ribosome production.

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