The nucleus is perhaps the most important structure inside animal and plant cells. It is the main control center for the cell and acts kind of like the cell's brain. Only eukaryotic cells have a nucleus. In fact, the definition of a eukaryotic cell is that it contains a nucleus while a prokaryotic cell is defined as not having a nucleus.
The nucleus is an organelle within the cell. This means it has a special function and is surrounded by a membrane that protects it from the rest of the cell. It floats within the cytoplasm (the fluid inside the cell).
How many nuclei are in a cell?
Most cells only have one nucleus. It would get confusing if there were two brains! However, there are some cells that develop with more than one nucleus. It's not common, but it does happen.
- Nuclear envelope - The nuclear envelope is made up of two separate membranes: the outer membrane and the inner membrane. The envelope protects the nucleus from the rest of the cytoplasm in the cell and keeps the special molecules within the nucleus from getting out.
- Nucleolus - The nucleolus is a large structure in the nucleus that mainly makes ribosomes and RNA.
- Nucleoplasm - The nucleoplasm is the liquid that fills the inside of the nucleus.
- Chromatin - Chromatin are composed of proteins and DNA. They organize into chromosomes prior to the cell dividing.
- Pore - The pores are small channels through the nuclear envelope. They allow for smaller molecules to pass through such as messenger RNA molecules, but keep larger DNA molecules inside the nucleus.
- Ribosome - Ribosomes are made inside the nucleolus and then sent outside the nucleus to make proteins.
The most important function of the nucleus is to store the cell's genetic information in the form of DNA. DNA holds the instructions for how the cell should work. DNA stands for deoxyribonucleic acid. The molecules of DNA are organized into special structures called chromosomes. Sections of DNA are called genes which hold hereditary information such as eye color and height. You can go here to learn more about DNA and chromosomes.
- RNA - In addition to DNA the nucleus holds another type of nucleic acid called RNA (ribonucleic acid). RNA plays an important role in making proteins called protein synthesis or translation.
- DNA replication - The nucleus can make exact copies of its DNA.
- Transcription - The nucleus makes RNA which can be used to carry messages and copies of DNA instructions.
- Translation - The RNA is used to configure amino acids into special proteins for use in the cell.
- The nucleus was the first of the cell organelles to be discovered by scientists.
- It usually takes up about 10 percent of the cell's volume.
- Each human cell contains around 6 feet of DNA which is tightly packed, but very organized with proteins.
- The nuclear envelope breaks down during cell division, but reforms after the two cells separate.
- Some scientists think that the nucleolus plays an important role in cell aging.
- The cell nucleus was given its name by Scottish Botanist Robert Brown.
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