The nucleus is defined as the organelle in cells that stores DNA and helps the cell make proteins.  It is often called the “control center” of the cell.  This is because it has instructions for all the other parts of the cell to do their jobs right.  It might help to think about of it like the “brain” of the cell.

computer image of cell with nucleus

When you see a picture of a cell, the nucleus looks like a big circular blob somewhere in the center of the cell.  Try to find the nucleus in the picture of the cell at the top of this page.  Remember that this is just an illustration and isn’t exactly what a real cell looks like.

It’s important to remember that animal cells and plant cells have nuclei, but bacteria cells don’t. Instead, their DNA just floats around the cell in a big clump.

Parts of the Nucleus

Shown below is a diagram of the nucleus, with all its parts labeled. You can find an explanation of each part listed below. Use the diagram to think about how all these parts can work together to perform the different functions of the nucleus.

Structure of Nucleus. parts of the cell nucleus: nuclear envelope, nucleoplasm, nuclear matrix, chromatin and nucleolus

Labeled diagram of the nucleus

Nucleolus: Makes ribosomes for the cell

Nucleoplasm: A jelly-like liquid made of water and other molecules (like the cytoplasm, but inside of the nucleus instead of outside)

Nuclear Lamina: Helps provide structure

Nuclear Envelope: Surrounds the nucleus and protects it (also called the nuclear membrane)

Chromatin: The way DNA is stored in the nuclei

Nuclear Pores: Small holes in the nuclear envelope where things can enter and exit

Ribosomes: Help make proteins (not technically part of the nuclei but some are attached to the outside of the nuclear envelope)



Functions of the Nucleus

Image showing DNA inside a cell nucleus

DNA stored as chromosomes in the nucleus

The nucleus is important for the cell because it contains the cell’s DNA, instructions for making all the proteins the cell needs.  It’s important that the DNA stays safe because without it the cell won’t be able to make proteins the right way.  The DNA never leaves the nucleus because then it wouldn’t be protected anymore.

Usually, DNA is stored as chromatin, which looks like bunched up string. But, when the cell is getting ready to divide, the DNA is stored as chromosomes, which look like little X’s.

The nucleus is also important because it controls the cell’s activities. It tells the cell when its time to make certain proteins and when to grow or reproduce.


Written by: Leah Tolby