Nucleus of the Cell

What is the nucleus of the cell?

Cells generally have three sections: the cell membrane or cell wall, the nucleus, and the cytoplasm. Arguably, the nucleus of the cell is the most important of all the structures in both plant and animal cells.

The difference between prokaryotic cells (simple cells, single-celled organisms) and eukaryotic (complex plant and animal cells) is that eukaryotic cells have a nucleus, while prokaryotic cells do not have nuclei.

The nucleus and nucleolus are found in the cytoplasm, but as its function is very different from the rest of the organelles, it has its own section. The nucleus has its own cell membrane, called a nuclear membrane, which separates it from the rest of the cytoplasm.

The purpose of the nucleus is to control the functioning of the cell, much like the brain controls the functioning of a human or animal. The fluid inside the nuclear membrane is called nucleoplasm.

Inside the nucleus, DNA (genetic material) is stored on chromatins. This information tells the cell how to form, what shape and size to grow into, and what functions to perform.

There is also a nucleolus inside the nucleus, a structure that contains RNA (another kind of genetic material made from DNA). Ribosomes that exist in the cytoplasm of the cell are created in the nucleolus.


What is the structure of the nucleus?

The nucleus contains several structures that help it function, just like the cell contains many different structures that help it function. The structures of the nucleus are very similar to the structures of the cell.

Structures of the nucleus include the nuclear envelope, the nucleolus, nucleoplasm, chromatins, and pores. The nuclear envelope is very similar to the cell membrane: it is a membranous structure that envelops the nucleus.

The nucleolus is a structure in the center of the nucleus that contains RNA, a type of genetic material made from DNA, and produces ribosomes. Nucleoplasm is the fluid inside the nuclear membrane, much like cytoplasm inside the cell membrane of a cell.

Chromatins are structures in the nucleus that contain proteins and genetic material, such as DNA. During the process of cell division, they help organize the replication process by condensing into chromosomes.

Finally, the pores of the nucleus are channels that exist within the nuclear envelope, similar to the protein channels that exist within the cell membrane and help substances pass into or out of the cell.

The pores of the nucleus are designed to allow very small molecules to pass through the nuclear envelope, such as RNA, but to keep larger genetic material, such as DNA, contained.

Nucleus of a Chironomus salivary gland cell

The cell nucleus during mitosis

During the second phase of mitosis, prophase, chromatins in the nucleus of the cell condense into the form of chromosomes, and the nuclear membrane begins breaking down.

During the fifth and last phase of mitosis, telophase, the cell creates two new nuclear membranes around each of the chromosome sets.

Once the two new nuclear membranes are created, then the wall of the parent cell will pinch together and create a split down the middle of the cell, creating two new daughter cells. The splitting process is called cytokinesis.

eukaryotic cell nucleus


  1. Which structure of the cell is the most important?
  2. Where is the nucleolus found?
  3. What is the purpose of the nucleus?
  4. Which structure of the human body is the nucleus of a cell most like?
  5. What is contained in the nucleolus?


  1. The nucleus of the cell is the most important structure.
  2. The nucleolus is found inside the nucleus of the cell.
  3. The purpose of the nucleus is to control the functioning of the cell.
  4. The nucleus of a cell is most like a human brain to a human body.
  5. The nucleolus contains RNA and produces ribosomes.