# Nucleus

The organelle that stores DNA and controls which genes are used. It is wrapped in a double membrane with pores that let molecules pass.

Biology (university) · Part 01: Cell structure and membranes · Card 3 of 9 · Last updated 2026-10-19

## Analogy

The head office that keeps the master plans and sends out copies.

## In practice

Messenger RNA is copied from DNA in the nucleus and leaves through the pores to be read in the cytoplasm.

## Practice

### Flashcards

- **What do nuclear pores do?** They let molecules such as messenger RNA and proteins pass between the nucleus and the cytoplasm.

### Interview questions

**Compare the structure of prokaryotic and eukaryotic cells and explain why compartments help eukaryotes.**

- Prokaryotes lack a nucleus and membrane-bound organelles
- Eukaryotes keep DNA in a nucleus and have organelles
- Compartments keep incompatible reactions apart
- Compartments raise efficiency by concentrating enzymes

## Questions people ask

### Why does the nucleus have a double membrane?

The double membrane gives the genome a strong barrier, separating DNA from the reactions in the cytoplasm. The outer layer connects to the endoplasmic reticulum. Nuclear pores cut through both layers, acting as gates that check which proteins and RNA are allowed to enter or leave.

### What is the nucleolus?

The nucleolus is a dense region inside the nucleus, not a separate organelle with its own membrane. It makes ribosomal RNA and assembles the two parts of ribosomes. Cells that make lots of protein, such as pancreas cells, usually have large and obvious nucleoli.

## Related concepts

- [Prokaryotic cell](https://studyvisually.com/learn/science/biology-university/biology-university-part-1/biology-university-part-1-concept-1)
- [Eukaryotic cell](https://studyvisually.com/learn/science/biology-university/biology-university-part-1/biology-university-part-1-concept-2)
- [Endomembrane system](https://studyvisually.com/learn/science/biology-university/biology-university-part-1/biology-university-part-1-concept-4)
- [Endosymbiosis](https://studyvisually.com/learn/science/biology-university/biology-university-part-1/biology-university-part-1-concept-5)

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