text stringlengths 4 7.07k | text_hash stringlengths 32 32 | __index_level_0__ int64 1 1.81M |
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Translocation of noisy miners is unlikely to be a solution to their overabundance in remnant habitats . In a Victorian study where birds were banded and relocated , colonies moved into the now unpopulated area but soon returned to their original territories . The translocated birds did not settle in a new territory . ... | 7325060ee754202786c30413cc7ca934 | 31,098 |
= Principe Amedeo @-@ class ironclad =
| 2beed0078700b3b475e47156b263cac3 | 31,101 |
The Principe Amedeo class was a pair of ironclad warships built for the Italian Regia Marina ( Royal Navy ) in the 1870s and 1880s . They were the culmination of a major naval construction program designed to give Italy a powerful fleet of ironclads . The two ships , Principe Amedeo and Palestro , were the last Italia... | e5b0ed60228a525c15dee9f4e75006fe | 31,103 |
= = Design = =
| 27a68d88afcf8b73909bed8e24598173 | 31,105 |
In 1862 , the Italian government under Prime Minister Urbano Rattazzi and his naval minister Carlo Pellion di Persano made the decision to build a fleet of ironclad warships . The Italian fleet had already acquired a pair of small , French @-@ built armored frigates of the Formidabile class , and two more vessels of t... | 5be7132eda1711e46e1bf48abedb65df | 31,107 |
= = = General characteristics and machinery = = =
| 91070e9a68f50dfb6e343cfa7764051d | 31,109 |
The two ships differed slightly in size . Principe Amedeo was 79 @.@ 73 meters ( 261 @.@ 6 ft ) long between perpendiculars , while Palestro was 78 @.@ 82 m ( 258 @.@ 6 ft ) long . Principe Amedeo had a beam of 17 @.@ 4 m ( 57 ft ) and a draft of 7 @.@ 9 m ( 26 ft ) ; Palestro 's beam measured 17 @.@ 3 m ( 57 ft ) , a... | 9fe816b27d7e4b28114a1a2ca8ec1dfc | 31,111 |
The ships ' propulsion system consisted of one single @-@ expansion steam engine that drove a single screw propeller , with steam supplied by six coal @-@ fired , cylindrical fire @-@ tube boilers . The boilers were trunked into a single funnel . The lead ship 's engine produced a top speed of 12 @.@ 2 knots ( 22 @.@ ... | 8e252ce9e9e6ae8bd5fa3d76da72743b | 31,112 |
= = = Armament and armor = = =
| 4ec93626b3a547980ff42f7fdb672b71 | 31,114 |
Palestro and Principe Amedeo were both armed with a main battery of six 10 in ( 254 mm ) guns , though they were mounted differently in each ship . Principe Amedeo carried hers in a single armored casemate located amidships , while Palestro 's guns were mounted in three armored casemates . The first was located forwar... | 8604ca61db0798a85927554f3be92bce | 31,116 |
The two ships were protected by iron belt armor that was 8 @.@ 7 in ( 221 mm ) thick and extended for the entire length of the hull . The casemates were protected with 5 @.@ 5 in ( 140 mm ) of iron plating , and the small conning tower had 2 @.@ 4 in ( 61 mm ) thick iron plates .
| 821ec14f98c1948df4daeb83ea72b4aa | 31,117 |
= = Ships = =
| a5e49ef500ca29a6008300510bc8e60a | 31,119 |
= = Service history = =
| 23e5a754ef5bf8e29b4df264b6ec61aa | 31,122 |
Neither ship had a particularly eventful career . They were completed too late to take part in the final stages of the wars of Italian unification . Instead , they were assigned to the Italian colonial empire , with occasional stints in the main Italian fleet . In 1880 , Palestro took part in a naval demonstration off... | 4ed077d6eb27185ecafa401e2a161acc | 31,124 |
In the late 1880s , both ships were withdrawn from frontline service and employed as headquarters ships for the defense of Taranto — Principe Amedeo — and La Maddalena — Palestro . Principe Amedeo was stricken from the naval register in 1895 and used as an ammunition depot ship in Taranto until 1910 , when she was sol... | 41e5caae84e8a2548bae3551333d3b3f | 31,125 |
= Cell nucleus =
| 2db6c49ca6892e9d98d6cd0307f287af | 31,128 |
In cell biology , the nucleus ( pl. nuclei ; from Latin nucleus or nuculeus , meaning kernel ) is a membrane @-@ enclosed 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 have many .
| da91095dada26a7ba1a1b3643db9747b | 31,130 |
Cell nuclei contain most of the cell 's genetic material , organized as multiple long 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 and are structured in such a way to promote cell function .... | 9c5649db6fa32a4af1c63330998dbf48 | 31,131 |
Because the nuclear membrane is impermeable to large molecules , nuclear pores are required that 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... | 3658a28e495fe889b58a71cb4472818f | 31,132 |
= = History = =
| fd3fc667e330e6e3944a4f085f9ef39d | 31,134 |
The nucleus was the first organelle to be discovered . What is most likely the 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... | 1676860717a91fa16d893c031fba246b | 31,136 |
The 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 under microscope when he observed an opaque area , which he called the " areola " or " nucleus " , in the cells of the flower 's out... | 98e491ad8aabb9dec47eb523b6bdcb87 | 31,137 |
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 ,... | 597a7b6a8e834360454ab16beb5a392f | 31,138 |
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 it was suggested that an individual develops from a ( single ) nucleated cell . This was in contradictio... | f0e002d0d015f861647f462a4625b36a | 31,139 |
= = Structures = =
| 48d6a981d19cdcb052568d567a42e96e | 31,141 |
The nucleus is the largest cellular organelle in animal cells . In mammalian cells , the average diameter of the nucleus is approximately 6 micrometres ( µm ) , which occupies about 10 % of the total cell volume . The viscous liquid within it is called nucleoplasm , and is similar in composition to the cytosol found o... | 866f9185797ce84262972cd35a153d19 | 31,143 |
= = = Nuclear envelope and pores = = =
| 57d3fb4b00e242a9c24bd4e1e001011c | 31,145 |
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 ( nm ) . The nuclear envelope completely encloses the nucleus and separates the cell 's genetic material from the surr... | a0723372c8c8f8d3930428594584b685 | 31,147 |
Nuclear pores , which provide aqueous channels through the envelope , are composed of multiple proteins , collectively referred to as nucleoporins . The pores are about 125 million daltons in molecular weight and consist of around 50 ( in yeast ) to several hundred proteins ( in vertebrates ) . The pores are 100 nm in... | 165531e71e987003e8c8fb2fc2004c51 | 31,148 |
Most proteins , ribosomal subunits , and some DNAs are transported through the pore complexes in a process mediated by a family of transport factors known as karyopherins . Those karyopherins that mediate movement into the nucleus are also called importins , whereas those that mediate movement out of the nucleus are c... | 3d7a972e4c1e3ce397cf02068072d707 | 31,149 |
= = = Nuclear lamina = = =
| 8090e94fd0cb8b80374d2375fff7632a | 31,151 |
In animal cells , two networks of intermediate filaments provide the nucleus with mechanical support : The nuclear lamina forms an organized meshwork on the internal face of the envelope , while less organized support is provided on the cytosolic face of the envelope . Both systems provide structural support for the n... | 394142daf7a3683fc7920f6f8267b82e | 31,153 |
The nuclear lamina is composed mostly of lamin proteins . Like all proteins , lamins are synthesized in the cytoplasm and later transported to the nucleus interior , where they are assembled before being incorporated into the existing network of nuclear lamina . Lamins found on the cytosolic face of the membrane , suc... | b0b99c72cee2058c90cda9f1e14bc437 | 31,154 |
Like the components of other intermediate filaments , the lamin monomer contains an alpha @-@ helical domain used by two monomers to coil around each other , forming a dimer structure called a coiled coil . Two of these dimer structures then join side by side , in an antiparallel arrangement , to form a tetramer calle... | 3dfb35ccd4dabad28cab2a4c19c0a1c4 | 31,155 |
Mutations in lamin genes leading to defects in filament assembly cause a group of rare genetic disorders known as laminopathies . The most notable laminopathy is the family of diseases known as progeria , which causes the appearance of premature aging in its sufferers . The exact mechanism by which the associated bioc... | 8cd8e03568f6613f83525134832c3ddb | 31,156 |
= = = Chromosomes = = =
| cc2f91d114a2dab280844317a7f1b9ce | 31,158 |
The cell nucleus contains the majority of the cell 's genetic material in the form of multiple linear DNA molecules organized into structures called chromosomes . Each human cell contains roughly two meters of DNA . During most of the cell cycle these are organized in a DNA @-@ protein complex known as chromatin , and... | a40cdef78789eebe7b2eb0da30d0a904 | 31,160 |
There are two types of chromatin . Euchromatin is the less compact DNA form , and contains genes that are frequently expressed by the cell . The other type , heterochromatin , is the more compact form , and contains DNA that is infrequently transcribed . This structure is further categorized into facultative heterochr... | b7c7956f2b030d2a72ff3cb322e756bc | 31,161 |
Antibodies to certain types of chromatin organization , in particular , nucleosomes , have been associated with a number of autoimmune diseases , such as systemic lupus erythematosus . These are known as anti @-@ nuclear antibodies ( ANA ) and have also been observed in concert with multiple sclerosis as part of gener... | 813f63df4f5a03a80a68f4446240d71d | 31,162 |
= = = Nucleolus = = =
| 47fc8ea3cf22df428f5e178f3a8cf3de | 31,164 |
The nucleolus is a discrete densely stained structure found in the nucleus . It is not surrounded by a membrane , and is sometimes called a suborganelle . It forms around tandem repeats of rDNA , DNA coding for ribosomal RNA ( rRNA ) . These regions are called nucleolar organizer regions ( NOR ) . The main roles of th... | a4e7284a648ccd44c42f179033374a47 | 31,166 |
In the first step of ribosome assembly , a protein called RNA polymerase I transcribes rDNA , which forms a large pre @-@ rRNA precursor . This is cleaved into the subunits 5.8S , 18S , and 28S rRNA . The transcription , post @-@ transcriptional processing , and assembly of rRNA occurs in the nucleolus , aided by smal... | fbf161fc57aac1913ff14a4878821238 | 31,167 |
When observed under the electron microscope , the nucleolus can be seen to consist of three distinguishable regions : the innermost fibrillar centers ( FCs ) , surrounded by the dense fibrillar component ( DFC ) , which in turn is bordered by the granular component ( GC ) . Transcription of the rDNA occurs either in t... | 4bdab847c35478949a05dd810f5551e0 | 31,168 |
= = = Other subnuclear bodies = = =
| dcf1bb9e48e3a112a7f2680090163df1 | 31,170 |
Besides the nucleolus , the nucleus contains a number of other non @-@ membrane @-@ delineated bodies . These include Cajal bodies , Gemini of coiled bodies , polymorphic interphase karyosomal association ( PIKA ) , promyelocytic leukaemia ( PML ) bodies , paraspeckles , and splicing speckles . Although little is know... | 6a74307faa7dd5fb5ba72eddbcfc9a55 | 31,172 |
Other subnuclear structures appear as part of abnormal disease processes . For example , the presence of small intranuclear rods has been reported in some cases of nemaline myopathy . This condition typically results from mutations in actin , and the rods themselves consist of mutant actin as well as other cytoskeleta... | e42d7ebf84a009902cce874d16aef644 | 31,173 |
= = = = Cajal bodies and gems = = = =
| bafa5ff999e4045eaeb00639adb89390 | 31,175 |
A nucleus typically contains between 1 and 10 compact structures called Cajal bodies or coiled bodies ( CB ) , whose diameter measures between 0 @.@ 2 µm and 2 @.@ 0 µm depending on the cell type and species . When seen under an electron microscope , they resemble balls of tangled thread and are dense foci of distribu... | 91666329d704c998295517d740c668cc | 31,177 |
Similar to Cajal bodies are Gemini of Cajal bodies , or gems , whose name is derived from the Gemini constellation in reference to their close " twin " relationship with CBs . Gems are similar in size and shape to CBs , and in fact are virtually indistinguishable under the microscope . Unlike CBs , gems do not contain... | ffee41d256c7677e0a0ba864b3d71101 | 31,178 |
= = = = RAFA and PTF domains = = = =
| b84d3041ada55a65e2d9800f51522656 | 31,180 |
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 discrete ... | 7017e914a242f898d6800aa78ba899c9 | 31,182 |
= = = = PML bodies = = = =
| 2918e4a7447c95bb9444877a11c37dcb | 31,184 |
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 their ... | 9bfbf7273149d6dabe7caea0931599b1 | 31,186 |
= = = = Splicing speckles = = = =
| 498ec9565c011a830589f8e4495fc457 | 31,188 |
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 examined... | f956664f58264b47002c5110b287a9be | 31,190 |
= = = = Paraspeckles = = = =
| c9cb9a871fe68b6e9b5b5fa7dd63e062 | 31,192 |
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 sections... | 6d0a0de410ee84341b3903d5b929e55a | 31,194 |
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 ) form a... | ae87053fec56e607d330c3ee4cc844ea | 31,195 |
= = = = Perichromatin fibrils = = = =
| 0d348d6d50548ba1ec9629d39caaa2ae | 31,197 |
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 .
| 0fcd6c94292d533454f3e2e4fba6ff3e | 31,199 |
= = Function = =
| 92a90101166ca1e918483a76bc9d157c | 31,201 |
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 cell ... | 1c4926d7dcaca10c21350ad097016898 | 31,203 |
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 .
| 3e8a34924bd3419de93326d77f46cee0 | 31,204 |
= = = Cell compartmentalization = = =
| 449c2b65de5d49913a70ed9ef62d2003 | 31,206 |
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 to th... | cad967634ec16841d4e648059c380bed | 31,208 |
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 example , ... | 3f7639761bf75f42c65db5e0bf04cd71 | 31,209 |
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 nucleus ,... | 14762d3a2c738104e2c92e74362b45eb | 31,210 |
= = = Gene expression = = =
| ae5d992f9844ee6e10c6689d9f53c81e | 31,212 |
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 nucleus , m... | 53cb343473842553b8bb58d7f8b2b89a | 31,214 |
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 synthe... | ef5a5d06161cda330e4be3ff8fcde723 | 31,215 |
= = = Processing of pre @-@ mRNA = = =
| 5582ef77662339ede7bad8c52b48407a | 31,217 |
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 . The t... | 37b6ed1c35aeb3e538d92691770b117f | 31,219 |
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 3 ' po... | c688e6f3e40e3acb17c9e3e1ee22d028 | 31,220 |
= = Dynamics and regulation = =
| c77b6cce3bacb0f95eaa90dee4558737 | 31,222 |
= = = Nuclear transport = = =
| e07fc1d3523e6d2875a29352e4666052 | 31,225 |
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 . " Cargo... | 9e60905121ab46445347119eac9a466c | 31,227 |
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 binds th... | c17f02e4e2aa282a653da217cb8c603d | 31,228 |
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 excisio... | c0aae21196eae21d73ef6fe220646011 | 31,229 |
= = = Assembly and disassembly = = =
| 729f977e37ce4a3a6a05cc20401d5f83 | 31,231 |
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 cells ... | f8f2fe8af68d1c4e2e39356d067fec57 | 31,233 |
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 the r... | 09c1c5495c21b59bd4ed9af98c5c5d66 | 31,234 |
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 other... | 18f7dea77c44785f5aca3cca5d7e52fe | 31,235 |
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 . The d... | ea63cb21d3b00ebd5460df2fe54f2670 | 31,236 |
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 the i... | a98da557e63db584d74bb88d8bbd2ab0 | 31,237 |
= = = Disease @-@ related dynamics = = =
| bdadc80286d36092df82f628bae5f3e8 | 31,239 |
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 .
| 91c16978e4f2892f56ccc2f03a949543 | 31,241 |
= = Nuclei per cell = =
| 72eac94c42ec5c3f5462a02bd62074c2 | 31,243 |
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 .
| 41f5126d6ed0e75c55719e0ebcaa5d55 | 31,245 |
= = = Anucleated cells = = =
| ed3785e79a047783576d15f729db3af4 | 31,247 |
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 from th... | 875e6ed11ddade71cb161ce946688349 | 31,249 |
In flowering plants , this condition occurs in sieve tube elements .
| 16c4278b3d84fef857470f6e6cd80f07 | 31,250 |
= = = Multinucleated cells = = =
| cf89d51d73de8d76aaf1dfa1ad6b34cc | 31,252 |
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 syncyti... | 4685d8805759f152621cc3719a6094c7 | 31,254 |
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 .
| bad1a3d91a12bfadf8af28151364a430 | 31,255 |
= = Evolution = =
| c785d063a39babd01b137eba17eaa867 | 31,257 |
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 .
| 6bc94b61dbd0b748ff422612640a2bcd | 31,259 |
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 archaea , ... | 4db53f076fa47ba5408b5dd3cabe0e1c | 31,260 |
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 that a ... | 83070d1fbba2a13634bb8be099c50d77 | 31,261 |
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 capping ... | fa37f695dd668b0e168c75d10fa17ef2 | 31,262 |
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 passag... | c6f34d149bae199eacbcf0f6be25094d | 31,263 |
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