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Scottish researcher Robert Brown (1773-1858) is considered the discoverer of the cell nucleus. Although many previous cytologists had already observed nuclei, they had not understood the enormous importance of these structures for cell life.
Brown's great merit was precisely to recognize the nucleus as a fundamental component of cells. The name he chose expresses this conviction: the word "core" comes from greek nuxwhich means seed. Brown imagined that the nucleus was the cell's seed by analogy to the fruits.
Today, we know that the nucleus is the center of control of cellular activity and the "archive" of hereditary information that the cell transmits to its daughters as it reproduces.
Eukaryotic and prokaryotic cells
The cell membrane is present in eukaryotic cells but absent in prokaryotes. In the eukaryotic cell, the hereditary material is separated from the cytoplasm by a membrane - the library - while in the prokaryotic cell the hereditary material is directly immersed in the cytoplasmic fluid.
The nucleus of cells that are not dividing presents a well-defined boundary due to nuclear membrane or library, visible only under the electron microscope.
Most of the nuclear volume is occupied by a filamentous mass called chromatin. There are still one or more dense bodies (nucleoli) and a viscous liquid (karyolymph or nucleoplasma).
We will study each of these components below.