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182.03575134277344 12 WikiText2 |
20150 RAFA domains , or polymorphic interphase karyosomal associations , were first described in microscopy studies in 1991 . Their function remains unclear , though they were not thought to be associated with active DNA replication , transcription , or RNA processing . They have been found to often associate with dis... |
80.85160064697266 73 WikiText2 |
20151 = = = = PML bodies = = = = |
107.708251953125 10 WikiText2 |
20152 Promyelocytic leukaemia bodies ( PML bodies ) are spherical bodies found scattered throughout the nucleoplasm , measuring around 0 @.@ 1 – 1 @.@ 0 µm . They are known by a number of other names , including nuclear domain 10 ( ND10 ) , Kremer bodies , and PML oncogenic domains . PML bodies are named after one of ... |
61.0639533996582 207 WikiText2 |
20153 = = = = Splicing speckles = = = = |
81.18948364257812 10 WikiText2 |
20154 Speckles are subnuclear structures that are enriched in pre @-@ messenger RNA splicing factors and are located in the interchromatin regions of the nucleoplasm of mammalian cells . At the fluorescence @-@ microscope level they appear as irregular , punctate structures , which vary in size and shape , and when ex... |
41.453208923339844 251 WikiText2 |
20155 = = = = Paraspeckles = = = = |
106.94739532470703 9 WikiText2 |
20156 Discovered by Fox et al. in 2002 , paraspeckles are irregularly shaped compartments in the nucleus ' interchromatin space . First documented in HeLa cells , where there are generally 10 – 30 per nucleus , paraspeckles are now known to also exist in all human primary cells , transformed cell lines , and tissue se... |
52.49421310424805 96 WikiText2 |
20157 Paraspeckles are dynamic structures that are altered in response to changes in cellular metabolic activity . They are transcription dependent and in the absence of RNA Pol II transcription , the paraspeckle disappears and all of its associated protein components ( PSP1 , p54nrb , PSP2 , CFI ( m ) 68 , and PSF ) ... |
52.51579284667969 122 WikiText2 |
20158 = = = = Perichromatin fibrils = = = = |
101.98584747314453 10 WikiText2 |
20159 Perichromatin fibrils are visible only under electron microscope . They are located next to the transcriptionally active chromatin and are hypothesized to be the sites of active pre @-@ mRNA processing . |
115.45929718017578 34 WikiText2 |
20160 = = Function = = |
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20161 The nucleus provides a site for genetic transcription that is segregated from the location of translation in the cytoplasm , allowing levels of gene regulation that are not available to prokaryotes . The main function of the cell nucleus is to control gene expression and mediate the replication of DNA during the... |
29.48988151550293 55 WikiText2 |
20162 The nucleus is an organelle found in eukaryotic cells . Inside its fully enclosed nuclear membrane , it contains the majority of the cell 's genetic material . This material is organized as DNA molecules , along with a variety of proteins , to form chromosomes . |
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20163 = = = Cell compartmentalization = = = |
140.748046875 8 WikiText2 |
20164 The nuclear envelope allows the nucleus to control its contents , and separate them from the rest of the cytoplasm where necessary . This is important for controlling processes on either side of the nuclear membrane . In most cases where a cytoplasmic process needs to be restricted , a key participant is removed... |
25.316444396972656 180 WikiText2 |
20165 In order to control which genes are being transcribed , the cell separates some transcription factor proteins responsible for regulating gene expression from physical access to the DNA until they are activated by other signaling pathways . This prevents even low levels of inappropriate gene expression . For exam... |
31.36805534362793 159 WikiText2 |
20166 The compartmentalization allows the cell to prevent translation of unspliced mRNA . Eukaryotic mRNA contains introns that must be removed before being translated to produce functional proteins . The splicing is done inside the nucleus before the mRNA can be accessed by ribosomes for translation . Without the nuc... |
36.36790466308594 67 WikiText2 |
20167 = = = Gene expression = = = |
138.61538696289062 8 WikiText2 |
20168 Gene expression first involves transcription , in which DNA is used as a template to produce RNA . In the case of genes encoding proteins , that RNA produced from this process is messenger RNA ( mRNA ) , which then needs to be translated by ribosomes to form a protein . As ribosomes are located outside the nucle... |
32.086395263671875 67 WikiText2 |
20169 Since the nucleus is the site of transcription , it also contains a variety of proteins that either directly mediate transcription or are involved in regulating the process . These proteins include helicases , which unwind the double @-@ stranded DNA molecule to facilitate access to it , RNA polymerases , which ... |
36.30942153930664 90 WikiText2 |
20170 = = = Processing of pre @-@ mRNA = = = |
702.916259765625 13 WikiText2 |
20171 Newly synthesized mRNA molecules are known as primary transcripts or pre @-@ mRNA . They must undergo post @-@ transcriptional modification in the nucleus before being exported to the cytoplasm ; mRNA that appears in the cytoplasm without these modifications is degraded rather than used for protein translation .... |
30.628173828125 140 WikiText2 |
20172 RNA splicing , carried out by a complex called the spliceosome , is the process by which introns , or regions of DNA that do not code for protein , are removed from the pre @-@ mRNA and the remaining exons connected to re @-@ form a single continuous molecule . This process normally occurs after 5 ' capping and ... |
39.97945785522461 133 WikiText2 |
20173 = = Dynamics and regulation = = |
1060.740966796875 7 WikiText2 |
20174 = = = Nuclear transport = = = |
313.7336120605469 8 WikiText2 |
20175 The entry and exit of large molecules from the nucleus is tightly controlled by the nuclear pore complexes . Although small molecules can enter the nucleus without regulation , macromolecules such as RNA and proteins require association karyopherins called importins to enter the nucleus and exportins to exit . "... |
25.518033981323242 179 WikiText2 |
20176 Nuclear import depends on the importin binding its cargo in the cytoplasm and carrying it through the nuclear pore into the nucleus . Inside the nucleus , RanGTP acts to separate the cargo from the importin , allowing the importin to exit the nucleus and be reused . Nuclear export is similar , as the exportin bi... |
38.559532165527344 84 WikiText2 |
20177 Specialized export proteins exist for translocation of mature mRNA and tRNA to the cytoplasm after post @-@ transcriptional modification is complete . This quality @-@ control mechanism is important due to these molecules ' central role in protein translation . Mis @-@ expression of a protein due to incomplete e... |
67.26891326904297 92 WikiText2 |
20178 = = = Assembly and disassembly = = = |
180.0364990234375 9 WikiText2 |
20179 During its lifetime , a nucleus may be broken down or destroyed , either in the process of cell division or as a consequence of apoptosis ( the process of programmed cell death ) . During these events , the structural components of the nucleus — the envelope and lamina — can be systematically degraded . In most ... |
20.47365379333496 187 WikiText2 |
20180 At a certain point during the cell cycle in open mitosis , the cell divides to form two cells . In order for this process to be possible , each of the new daughter cells must have a full set of genes , a process requiring replication of the chromosomes as well as segregation of the separate sets . This occurs by... |
22.8043155670166 217 WikiText2 |
20181 However , in dinoflagellates , the nuclear envelope remains intact , the centrosomes are located in the cytoplasm , and the microtubules come in contact with chromosomes , whose centromeric regions are incorporated into the nuclear envelope ( the so @-@ called closed mitosis with extranuclear spindle ) . In many... |
45.07213592529297 83 WikiText2 |
20182 Apoptosis is a controlled process in which the cell 's structural components are destroyed , resulting in death of the cell . Changes associated with apoptosis directly affect the nucleus and its contents , for example , in the condensation of chromatin and the disintegration of the nuclear envelope and lamina .... |
28.936477661132812 151 WikiText2 |
20183 The nuclear envelope acts as a barrier that prevents both DNA and RNA viruses from entering the nucleus . Some viruses require access to proteins inside the nucleus in order to replicate and / or assemble . DNA viruses , such as herpesvirus replicate and assemble in the cell nucleus , and exit by budding through... |
38.470542907714844 79 WikiText2 |
20184 = = = Disease @-@ related dynamics = = = |
646.1804809570312 12 WikiText2 |
20185 Initially , it has been suspected that immunoglobulins in general and autoantibodies in particular do not enter the nucleus . Now there is a body of evidence that under pathological conditions ( e.g. lupus erythematosus ) IgG can enter the nucleus . |
15.532254219055176 43 WikiText2 |
20186 = = Nuclei per cell = = |
170.22898864746094 7 WikiText2 |
20187 Most eukaryotic cell types usually have a single nucleus , but some have no nuclei , while others have several . This can result from normal development , as in the maturation of mammalian red blood cells , or from faulty cell division . |
29.63558578491211 44 WikiText2 |
20188 = = = Anucleated cells = = = |
171.42445373535156 8 WikiText2 |
20189 An anucleated cell contains no nucleus and is , therefore , incapable of dividing to produce daughter cells . The best @-@ known anucleated cell is the mammalian red blood cell , or erythrocyte , which also lacks other organelles such as mitochondria , and serves primarily as a transport vessel to ferry oxygen f... |
21.110671997070312 153 WikiText2 |
20190 In flowering plants , this condition occurs in sieve tube elements . |
894.7578735351562 12 WikiText2 |
20191 = = = Multinucleated cells = = = |
128.05580139160156 8 WikiText2 |
20192 Multinucleated cells contain multiple nuclei . Most acantharean species of protozoa and some fungi in mycorrhizae have naturally multinucleated cells . Other examples include the intestinal parasites in the genus Giardia , which have two nuclei per cell . In humans , skeletal muscle cells , called myocytes and s... |
26.961257934570312 115 WikiText2 |
20193 A number of dinoflagelates are known to have two nuclei . Unlike other multinucleated cells these nuclei contain two distinct lineages of DNA : one from the dinoflagelate and the other from a symbiotic diatom . Curiously the mitochondrion and the plastid of the diatom remain functional . |
42.23710250854492 48 WikiText2 |
20194 = = Evolution = = |
758.5618896484375 5 WikiText2 |
20195 As the major defining characteristic of the eukaryotic cell , the nucleus ' evolutionary origin has been the subject of much speculation . Four major hypotheses have been proposed to explain the existence of the nucleus , although none have yet earned widespread support . |
35.11695861816406 45 WikiText2 |
20196 The first model known as the " syntrophic model " proposes that a symbiotic relationship between the archaea and bacteria created the nucleus @-@ containing eukaryotic cell . ( Organisms of the Archaea and Bacteria domain have no cell nucleus . ) It is hypothesized that the symbiosis originated when ancient arch... |
27.902700424194336 169 WikiText2 |
20197 A second model proposes that proto @-@ eukaryotic cells evolved from bacteria without an endosymbiotic stage . This model is based on the existence of modern planctomycetes bacteria that possess a nuclear structure with primitive pores and other compartmentalized membrane structures . A similar proposal states t... |
62.691001892089844 76 WikiText2 |
20198 The most controversial model , known as viral eukaryogenesis , posits that the membrane @-@ bound nucleus , along with other eukaryotic features , originated from the infection of a prokaryote by a virus . The suggestion is based on similarities between eukaryotes and viruses such as linear DNA strands , mRNA ca... |
35.04118347167969 143 WikiText2 |
20199 A more recent proposal , the exomembrane hypothesis , suggests that the nucleus instead originated from a single ancestral cell that evolved a second exterior cell membrane ; the interior membrane enclosing the original cell then became the nuclear membrane and evolved increasingly elaborate pore structures for ... |
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