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Nucleolus facts for kids

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Photomicrograph of nucleus and nucleolus

A nucleolus (plural: nucleoli) is the part of a eukaryote cell where ribosomes are made. Viewed through a microscope, the nucleolus appears as a dark spot inside the cell's nucleus. It is made up of dense RNA and proteins. Prokaryote cells have ribosomes, but they don't make as many as eukaryotes do, and there is no visible nucleolus. There is usually more than one nucleolus in a eukaryote cell.

The nucleolus is made at a nucleolus organizer region (NOR), which is a chromosome region around which the nucleolus forms. Inside the nucleolus ribosomes are made. Ribosomes are molecular machines that synthesize proteins. The ribosomes are exported through the nuclear envelope to the cytoplasm, where they do their work.

Nucleoli also have other important functions like assembly of signal recognition particles and playing a role in the cell's response to stress. Malfunction of nucleoli can be the cause of several human diseases.

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