# The Cell Nucleus

> The nucleus is the cell's control room. A double membrane with pores wraps the chromatin, and inside sits the nucleolus where ribosome parts are built. It connects directly to the rough endoplasmic reticulum.

Web page: https://cellnaut.com/topics/nucleus

![Teaching illustration: The Cell Nucleus](https://cellnaut.com/topic-illustrations/nucleus-teaching.jpg)

## Labelled parts

1. **Nuclear envelope**: Two membranes that separate the DNA from the cytoplasm; the outer one joins the endoplasmic reticulum.
2. **Nuclear pores**: Protein-lined channels that control what goes in and out, such as messenger RNA leaving.
3. **Nucleolus**: A dense region that builds ribosome subunits.
4. **Chromatin**: Thread-like DNA and protein; tightly packed parts are less active, loose parts are being read.
5. **Rough endoplasmic reticulum**: Folded membrane sheets continuous with the outer nuclear membrane.
6. **Ribosomes**: Small particles on the rough ER that build proteins from messenger RNA.

## Key points

- The nuclear envelope has two membranes and many pores that let RNA and proteins pass.
- Chromatin is DNA wrapped around proteins; it coils up into chromosomes before division.
- The nucleolus is where ribosomal RNA is made and combined with proteins into ribosome subunits.

## Check yourself

**1. What is the job of the nucleolus?**

- A. Make ATP
- B. Build ribosome subunits
- C. Digest waste
- D. Store water

**Answer:** B. Build ribosome subunits - Ribosomal RNA is made in the nucleolus and joins proteins there.

**2. What lets messenger RNA leave the nucleus?**

- A. Nuclear pores
- B. Mitochondria
- C. Lysosomes
- D. The cell wall

**Answer:** A. Nuclear pores - Messenger RNA travels out through nuclear pores to meet ribosomes.

## Related lessons

- [The Nucleus and the Endomembrane System](https://cellnaut.com/learn/nucleus-and-endomembrane)
- [From DNA to Protein](https://cellnaut.com/learn/dna-to-protein)

## See it in 3D

- [Animal Cell](https://cellnaut.com/studio/animal)
- [Stem Cell](https://cellnaut.com/studio/stem)

Explanations rewritten in our own words from Biology 2e, Chapter 4: Cell Structure (OpenStax), licensed CC BY-NC-SA 4.0. https://openstax.org/books/biology-2e/pages/4-introduction