The nucleolus is found in the nucleus of a cell and appears as a dark spherical region when seen through a microscope. The nucleolus is one of the largest physical structures within the nucleus and can occupy up to a quarter of its total volume.
The nucleolus largely consists of proteins and RNA. It is a very dense cellular structure that was first discovered in the 1700s when the nucleus of molecules began being studied in detail using microscopes. It wasn't until many years later, however, that the function of the nucleolus was discovered.
The primary purpose of the nucleolus is to produce the components of ribosomes. These are used by the cell to produce different types of protein and are essential for cells to survive and function. Ribosomes are produced by combining RNA, which is a special type of molecule involved in protein production, with other types of protein.
Different cells require varying amounts of protein. The more protein that a cell needs, the larger the nucleolus is likely to be. This is because generating larger amounts of proteins requires considerably more ribosomes. Certain types of cells may also have more than one nucleolus depending on the cell’s ribosome production requirements.