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In cell biology, the nucleus (pl. nuclei; from Latin nucleus or nuculeus, meaning kernel), also sometimes referred to as the "control center", is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material, organized as multiplelong linear DNA molecules in complex with a large variety of proteins, such as histones, to form chromosomes. The genes within these chromosomes are the cell's nuclear genome. The function of the nucleus is to maintain the integrity of these genes and to control the activities of the cell by regulating gene expression — the nucleus is therefore the control center of the cell.
HeLa cells stainedfor DNA with the Blue Hoechst dye. The central and rightmost cell are in interphase, thus their entire nuclei are labeled. On the left a cell is going through mitosis and its DNA has condensed ready for division.
The main structures making up the nucleus are the nuclear envelope, a double membrane that encloses the entire organelle and separates its contents from the cellular cytoplasm, and thenuclear lamina, a meshwork within the nucleus that adds mechanical support, much like the cytoskeleton supports the cell as a whole. Because the nuclear membrane is impermeable to most molecules, nuclear pores are required to allow movement of molecules across the envelope. These pores cross both of the Schematic of typical animal cell, showing subcellular components. Organelles: (1) nucleolus(2) nucleus (3) ribosome (4) vesicle (5) rough endoplasmic reticulum (ER) (6) membranes, providing a channel that Golgi apparatus (7) Cytoskeleton (8) smooth ER (9) mitochondria (10) vacuole (11) allows free movement of small cytoplasm (12) lysosome (13) centrioles molecules and ions. The movement of larger molecules such as proteins is carefully controlled, and requires active transport regulatedby carrier proteins. Nuclear transport is crucial to cell function, as movement through the pores is required for both gene expression and chromosomal maintenance.
Although the interior of the nucleus does not contain any membrane-bound subcompartments, its contents are not uniform, and a number of subnuclear bodies exist, made up of unique proteins, RNA molecules, andparticular parts of the chromosomes. The best known of these is the nucleolus, which is mainly involved in the assembly of ribosomes. After being produced in the nucleolus, ribosomes are exported to the cytoplasm where they translate mRNA.
Entry of material into the nucleus through phagocytosis. The phagosome travels from the cell membrane to the nucleus, and then is engulfed by the nucleus,releasing its contents.
The nucleus was the first organelle to be discovered. The probably oldest preserved drawing dates back to the early microscopist Antonie van Leeuwenhoek (1632 – 1723). He observed a "Lumen", the nucleus, in the red blood cells of salmon . Unlike mammalian red blood cells, those of other vertebrates still possess nuclei. The Oldest known depiction of cells and theirnuclei by Antonie van Leeuwenhoek, 1719. nucleus was also described by Franz Bauer in 1804 and in more detail in 1831 by Scottish botanist Robert Brown in a talk at the Linnean Society of London. Brown was studying orchids microscopically when he observed an opaque area, which he called the areola or nucleus, in the cells of the flower's outer layer. He did not suggest a potential function.In 1838 Matthias Schleiden proposed that the nucleus plays a role in generating cells, thus he introduced the name "Cytoblast" (cell builder). He believed that he had observed new cells assembling around "cytoblasts". Franz Meyen was a strong opponent of this view having already described cells multiplying by division and Drawing of a Chironomus salivary gland cell believing that many cells would...