Cell nucleus

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Cells in tissue culture stained for DNA with the blue Hoechst dye. The middle and right cells are in interphase, so their entire nuclei are labeled. On the left, a cell is going through mitosis and its DNA has condensed, ready for division
The eukaryotic cell nucleus. Seen here are the ribosome-dotted double membranes of the nuclear envelope, the DNA complex, and the nucleolus

The cell nucleus​ (plural: cell nuclei) is a membrane bound structure that contains the cell's genes and controls the cell's growth and reproduction. It is usually the most prominent organelle in a cell. The nucleus is small and round, and it works as the cell's control center. It contains chromosomes which house the DNA. The human body contains billions of cells, most of which have a nucleus.

All eukaryote organisms have nuclei in their cells, even the many eukaryotes that are single-celled. Bacteria and Archaea, which are prokaryotes, are single-celled organisms of quite a different type and do not have nuclei. Cell nuclei were first found by Antonie van Leeuwenhoek in the 17th century.

The nucleus has a membrane around it but the things inside it do not. Inside it are many proteins, RNA molecules, chromosomes and the nucleolus. In the nucleolus ribosomes are put together. After being produced in the nucleolus, ribosomes are exported to the cytoplasm where they translate mRNA into proteins.

When a cell is dividing or preparing to divide, the chromosomes become visible with a light microscope. At other times when the chromosomes are not visible, the nucleolus will be visible.

Nuclear membrane[change | change source]

A double-layer nuclear membrane covers the nucleus. Large molecules cannot get through; it is impermeable to them. However, the membrane has nuclear pores that allow and control the movement of molecules across across both membranes. The larger molecules are actively transported by carrier proteins, and there is free movement of small molecules and ions. Large molecules such as proteins and RNA must go through the pores, to do their jobs of gene expression and the maintenance of chromosomes.

Nucleolus[change | change source]

Within the nucleus is a structure called a nucleolus. It is made at a nucleolus organizer region (NOR), which is a chromosomal region around which the nucleolus forms. Inside the nucleolus ribosomes are made. These are exported through the nuclear pore complexes to the cytoplasm, where they are work to build proteins and sometimes become attached to the endoplasmic reticulum if they are making membrane proteins.[1]

References[change | change source]

  1. Cooper, Geoffrey M.; Hausman, Robert E. (2007). The Cell: a molecular approach (4th ed.). Sinauer Associates. pp. 371–9. ISBN 0878932208.