Cell nucleus

In cell biology, the nucleus is a membrane-bound organelle found in eukaryotic cells. Eukaryotes usually have a single nucleus, but a few cell types, such as mammalian red blood cells, have no nuclei. The cell nucleus contains all of the cell’s genome, except for a small fraction of mitochondrial DNA.

About Cell nucleus in brief

In cell biology, the nucleus is a membrane-bound organelle found in eukaryotic cells. Eukaryotes usually have a single nucleus, but a few cell types, such as mammalian red blood cells, have no nuclei, and a few others including osteoclasts have many. The cell nucleus contains all of the cell’s genome, except for a small fraction of mitochondrial DNA, organized as multiple long linear DNA molecules in a complex with a large variety of proteins. The genes within these chromosomes are structured in such a way to promote cell function. The nucleus of a typical mammalian cell will have about 3000 to 4000 pores throughout its nucleus, each of each of which contains an eight-fold-shaped ring-shaped structure at a position where the inner and outer membranes fuse into a basket. Most proteins, including ribosomes and DNAs, are transported through the pore complexes in a process known as transport by a family of factors mediated by a process called pore-mediated transport (PRT) The nuclear matrix is a network within the nucleus that adds mechanical support, much like the cytoskeleton supports the cell as a whole. The nuclear envelope is a double membrane that encloses the entire organelle and isolates its contents from the cellular cytoplasm. It is impermeable to large molecules, so nuclear pores are required to regulate nuclear transport of molecules across the envelope. The pores cross both nuclear membranes, providing a channel through which larger molecules must be actively transported by carrier proteins while allowing free movement of small molecules and ions.

This size allows the passage of water-soluble molecules while preventing larger molecules such as nucleic acids and larger proteins, from being inappropriately transported into the nucleus. The size of the nucleus depends on the size of a cell it is contained in, with a nucleus typically occupying about 8% of the total cell volume. The nucleus is the largest organelle in animal cells, with an average diameter of approximately 6 micrometres. The inner membrane surrounds the nuclear content, providing its defining edge. Embedded within the inner membrane, various proteins bind the intermediate filaments that give the nucleus its structure. The outer membrane both envelopes the inner membranes, and is continuous with the adjacent endoplasmic reticulum membrane. The space between the two membranes, called the perinuclear space, is continuous. : 649 The outer nuclear membrane is studded with ribosome that are actively translating proteins across membrane. Despite their close apposition around much of. the nucleus, its contents are not uniform, and there are a number of nuclear bodies exist, made up of unique proteins, RNA molecules, and particular 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 nuclelus, ribosoms are exported to the cy toplasm where they translate mRNA. A number of these are known to serve to mediate transport of nuclear transport proteins.

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