In cell biology, the nucleus is a membrane-bound organelle found in eukaryotic cells. Eukaryotes have a single nucleus, but a few cell types, such as mammalian red blood cells, have no nuclei, 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, such as histones, to form chromosomes. The genes within these chromosomes are structured in such a way to promote cell function; the nucleus maintains the integrity of genes and controls the activities of the cell by regulating gene expression—the nucleus is, the control center of the cell. The main structures making up the nucleus are the nuclear envelope, a double membrane that encloses the entire organelle and isolates its contents from the cellular cytoplasm, the nuclear matrix, a network within the nucleus that adds mechanical support, much like the cytoskeleton, which supports the cell as a whole.
Because the nuclear envelope is impermeable to large molecules, 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 transported by carrier proteins while allowing free movement of small molecules and ions. Movement of large molecules such as proteins and RNA through the pores is required for both gene expression and the maintenance of chromosomes. Although the interior of the nucleus does not contain any membrane-bound subcompartments, its contents are not uniform, a number of nuclear bodies exist, made up of unique proteins, RNA molecules, particular parts of the chromosomes; the best-known of these is the nucleolus, involved in the assembly of ribosomes. After being produced in the nucleolus, ribosomes are exported to the cytoplasm where they translate mRNA; the nucleus was the first organelle to be discovered. What is most the oldest preserved drawing dates back to the early microscopist Antonie van Leeuwenhoek.
He observed the nucleus, in the red blood cells of salmon. Unlike mammalian red blood cells, those of other vertebrates still contain nuclei; the nucleus was 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 under the microscope 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", he believed that he had observed new cells assembling around "cytoblasts". Franz Meyen was a strong opponent of this view, having described cells multiplying by division and believing that many cells would have no nuclei; the idea that cells can be generated de novo, by the "cytoblast" or otherwise, contradicted work by Robert Remak and Rudolf Virchow who decisively propagated the new paradigm that cells are generated by cells.
The function of the nucleus remained unclear. Between 1877 and 1878, Oscar Hertwig published several studies on the fertilization of sea urchin eggs, showing that the nucleus of the sperm enters the oocyte and fuses with its nucleus; this was the first time. This was in contradiction to Ernst Haeckel's theory that the complete phylogeny of a species would be repeated during embryonic development, including generation of the first nucleated cell from a "monerula", a structureless mass of primordial protoplasm. Therefore, the necessity of the sperm nucleus for fertilization was discussed for quite some time. However, Hertwig confirmed his observation in other animal groups, including amphibians and molluscs. Eduard Strasburger produced the same results for plants in 1884; this paved the way to assign the nucleus an important role in heredity. In 1873, August Weismann postulated the equivalence of the maternal and paternal germ cells for heredity; the function of the nucleus as carrier of genetic information became clear only after mitosis was discovered and the Mendelian rules were rediscovered at the beginning of the 20th century.
The nucleus is the largest organelle in animal cells. In mammalian cells, the average diameter of the nucleus is 6 micrometres, which occupies about 10% of the total cell volume; the contents of the nucleus are held in the nucleoplasm similar to the cytoplasm in the rest of the cell. The fluid component of this is termed the nucleosol, similar to the cytosol in the cytoplasm. In most types of granulocyte, a white blood cell, the nucleus is lobated and can be bi-lobed, tri-lobed or multi-lobed; the nuclear envelope, otherwise known as nuclear membrane, consists of two cellular membranes, an inner and an outer membrane, arranged parallel to one another and separated by 10 to 50 nanometres. The nuclear envelope encloses the nucleus and separates the cell's genetic material from the surrounding cytoplasm, serving as a barrier to prevent macromolecules from diffusing between the nucleoplasm and the cytoplasm; the outer nuclear membrane is continuous with the membrane of the rough endoplasmic reticulum, is studded with ribosomes.
The space between the membranes is called the perinuclear space and is continuous with the RER lumen. Nuclear pores, which provide aqueous
Voden Heights are the heights extending 42.5 km in east-west direction and 15.4 km wide, rising to 1650 m on Oscar II Coast in Graham Land. They are bounded by Flask Glacier to the north, Scar Inlet to the east, Leppard Glacier to the south and its tributary Fleece Glacier to the southwest, linked by a wide ice-covered saddle to Bruce Plateau to the west; the feature is named after the settlements of Voden in Northeastern and Southern Bulgaria. Voden Heights are centred at 65°50′40″S 62°50′40″W. British mapping in 1976. British Antarctic Territory. Scale 1:200000 topographic map. DOS 610 Series, Sheet W 65 62. Directorate of Overseas Surveys, Tolworth, UK, 1976. Antarctic Digital Database. Scale 1:250000 topographic map of Antarctica. Scientific Committee on Antarctic Research. Since 1993 upgraded and updated. Voden Heights. SCAR Composite Antarctic Gazetteer. Bulgarian Antarctic Gazetteer. Antarctic Place-names Commission. Voden Heights. Copernix satellite image This article includes information from the Antarctic Place-names Commission of Bulgaria, used with permission
Malcolm Winters is a fictional character from the American CBS soap opera, The Young and the Restless. And most portrayed by Shemar Moore, Darius McCrary took over between December 29, 2009, October 17, 2011. Moore reprised the role for a guest appearance in September 2014 and April 2019. Malcolm is the half-brother of Neil Winters, his history includes getting Neil's wife, Drucilla Winters, his history as a photographer, marriages to Olivia Winters and Sofia Dupre. In March 2019, it was announced that Moore would reprise the role of Malcolm Winters for a two-episode stint, following St. John's passing the month before; the role was originated by Shemar Moore on May 5, 1994, who received a Daytime Emmy Award for Outstanding Supporting Actor for his portrayal in 2000, with nominations for Outstanding Younger Actor in 1996 and 1997. After much speculation that Moore would exit the soap opera in 2000, he confirmed that he would depart at the end of his contract in the spring of 2001. However, in February 2001, Moore announced that he had extended his contract through the end of that year.
In December, he announced he was leaving The Young and the Restless, last aired on February 14, 2002. In September 2004, after a two-year absence, Moore was announced to reprise the role. Of Moore's return, former co-head writer John F. Smith stated: "We are thrilled to have Shemar back with us, his story will be something unexpected, off the page, exciting. The man is going to have impact." Moore made his return on November 1, 2004. However, within weeks, Moore's publicist revealed that his return would be short-lived, as he had only signed a six-month contract; the publicist stated: "he has two or three films coming out next year. You know. At least have him for six months." Moore made his final appearance as the character on September 1, 2005. In September 2009, it was announced that the soap opera had put out a casting call for the role of Malcolm. In November, Darius McCrary was announced to be joining the cast, in his first daytime television role, with his first appearance on December 29, 2009.
In September 2011, it was announced. He made his final appearance on October 17, 2011. On July 23, 2014, CBS Daytime announced that Moore would reprise the role of Malcolm for a two-episode guest stint starting on September 10, 2014. In March 2019, it was announced that Moore would return for another two-episode guest stint, following the death of Kristoff St. John. Malcolm first arrives in Genoa City in 1994, determined to get to know his estranged half-brother, Neil Winters. Neil, at first, wants nothing to do with his rebellious younger half-brother, but decides to give him a second chance. With the help of Blade Bladeson, Malcolm became Genoa City's most prominent photographer, he develops a friendship with Neil's wife Drucilla Barber, is smitten with her, but nothing becomes of it. However, Malcolm discovers Drucilla after she has taken a good dose of cold medication, thus mistakes Malcolm for Neil. After Drucilla calls out for Neil, making Malcolm realize her advances were not intended for him, Malcolm chooses to rape her.
The following morning, Malcolm realizes what a mistake he has made and confides his crime to Dru's sister, Olivia. Nine months Drucilla gives birth to a daughter, Lily Winters. Having convinced herself that Neil is Lily's father, Dru forgives Malcolm and Olivia soon fixes him up with her hospital colleague, Keesha Monroe, they fall in love and marry, just before Keesha dies of AIDS. Malcolm develops a relationship with widowed Olivia and grows attached to her son Nathan Hastings, Jr. Malcolm and Olivia marry in 1997. One year Malcolm's ex-girlfriend Callie Rogers arrives in town and Olivia becomes jealous that Malcolm is spending so much time with her. Olivia's insecurity destroys her marriage to Malcolm and he rebounds back to Callie; the two become engaged but Callie soon breaks it off and leaves town. In the meantime, Malcolm continues his close relationship with his former stepson Nate, who views Malcolm as his father. Malcolm and Neil soon find themselves fighting over attorney Alex Perez.
Malcolm and Alex fall in love and become engaged, though she is developing feelings for Neil. While the three of them are on business in Kenya, Malcolm leaves. While driving over a bridge, on the way to a photo shoot, the bridge collapses and Malcolm is presumed dead. Malcolm returns to town two years resenting Neil, believing he did not do enough to rescue him in Kenya; the two bury the hatchet. While in town, Malcolm has a fling with Adrienne Markham, Damon Porter's ex-wife. Malcolm demands that Dru take a paternity test to determine once and for all if he is Lily's biological father; when Malcolm is proven to be Lily's father, he and Dru decide to keep it a secret and he leaves town. While Malcolm is gone and Neil discover the truth about her paternity, but are unable to contact him. Four years Malcolm returned to Genoa City while secretly working undercover as a corporate spy for Tucker McCall, he learns that Lily had been diagnosed with ovarian cancer and attempted to support her while clashing with Neil.
However, the two put aside their differences and reconnected as brothers. Malcolm took a job as a photographer at Restless Style magazine and hired his adopted nephew, Devon Hamilton, as his assistant. Months after Malcolm mentioned he was engaged, Sofia Dupre, arrived in town, she worked for Tucker and had a business clash with Neil, they ended up havin