3T1I
43-464: The Mre11 family of enzymes includes: MRE11A in humans The Mre11 in Pyrococcus furiosus - see Pyrococcus furiosus § Mre11 Topics referred to by the same term [REDACTED] This disambiguation page lists articles associated with the title Mre11 . If an internal link led you here, you may wish to change the link to point directly to
86-409: A haploid chromosomal composition that is partially replicated, a condition known as merodiploidy . Prokaryotes lack mitochondria and chloroplasts . Instead, processes such as oxidative phosphorylation and photosynthesis take place across the prokaryotic cell membrane . However, prokaryotes do possess some internal structures, such as prokaryotic cytoskeletons . It has been suggested that
129-693: A paraphyletic group, just like dinosaurs without birds. Unlike the above assumption of a fundamental split between prokaryotes and eukaryotes, the most important difference between biota may be the division between Bacteria and the rest (Archaea and Eukaryota). For instance, DNA replication differs fundamentally between the Bacteria and Archaea (including that in eukaryotic nuclei), and it may not be homologous between these two groups. Moreover, ATP synthase , though common (homologous) in all organisms, differs greatly between bacteria (including eukaryotic organelles such as mitochondria and chloroplasts ) and
172-1088: A prokaryotic cytoskeleton that is more primitive than that of the eukaryotes. Besides homologues of actin and tubulin ( MreB and FtsZ ), the helically arranged building-block of the flagellum , flagellin , is one of the most significant cytoskeletal proteins of bacteria, as it provides structural backgrounds of chemotaxis , the basic cell physiological response of bacteria. At least some prokaryotes also contain intracellular structures that can be seen as primitive organelles. Membranous organelles (or intracellular membranes) are known in some groups of prokaryotes, such as vacuoles or membrane systems devoted to special metabolic properties, such as photosynthesis or chemolithotrophy . In addition, some species also contain carbohydrate-enclosed microcompartments, which have distinct physiological roles (e.g. carboxysomes or gas vacuoles). Most prokaryotes are between 1 μm and 10 μm, but they can vary in size from 0.2 μm ( Mycoplasma genitalium ) to 750 μm ( Thiomargarita namibiensis ). Prokaryotic cells have various shapes;
215-401: A taxon to be found nearby the then-unknown Asgard group). For example, histones which usually package DNA in eukaryotic nuclei, have also been found in several archaean groups, giving evidence for homology . This idea might clarify the mysterious predecessor of eukaryotic cells ( eucytes ) which engulfed an alphaproteobacterium forming the first eucyte ( LECA , l ast e ukaryotic c ommon
258-474: A DNA repair enzyme results in increased un-repaired DNA damages which, through replication errors ( translesion synthesis ), lead to mutations and cancer. However, MRE11 mediated MMEJ repair is highly inaccurate, so in this case, over-expression, rather than under-expression, apparently leads to cancer. MRE11 has been shown to interact with: Prokaryote A prokaryote ( / p r oʊ ˈ k ær i oʊ t , - ə t / ; less commonly spelled procaryote )
301-1203: A bacterium to bind, take up and recombine donor DNA into its own chromosome, it must first enter a special physiological state called competence . About 40 genes are required in Bacillus subtilis for the development of competence. The length of DNA transferred during B. subtilis transformation can be as much as a third to the whole chromosome. Transformation is a common mode of DNA transfer, and 67 prokaryotic species are thus far known to be naturally competent for transformation. Among archaea, Halobacterium volcanii forms cytoplasmic bridges between cells that appear to be used for transfer of DNA from one cell to another. Another archaeon, Sulfolobus solfataricus , transfers DNA between cells by direct contact. Frols et al. (2008) found that exposure of S. solfataricus to DNA damaging agents induces cellular aggregation, and suggested that cellular aggregation may enhance DNA transfer among cells to provide increased repair of damaged DNA via homologous recombination. While prokaryotes are considered strictly unicellular, most can form stable aggregate communities. When such communities are encased in
344-653: A complex with the RAD50 homolog; this complex is required for nonhomologous joining of DNA ends and possesses increased single-stranded DNA endonuclease and 3' to 5' exonuclease activities. In conjunction with a DNA ligase , this protein promotes the joining of noncomplementary ends in vitro using short homologies near the ends of the DNA fragments. This gene has a pseudogene on chromosome 3 . Alternative splicing of this gene results in two transcript variants encoding different isoforms. Mre11, an ortholog of human MRE11, occurs in
387-399: A higher metabolic rate , a higher growth rate, and as a consequence, a shorter generation time than eukaryotes. There is increasing evidence that the roots of the eukaryotes are to be found in (or at least next to) the archaean Asgard group, perhaps Heimdallarchaeota (an idea which is a modern version of the 1984 eocyte hypothesis , eocytes being an old synonym for Thermoproteota ,
430-527: A ncestor) according to endosymbiotic theory . There might have been some additional support by viruses, called viral eukaryogenesis . The non-bacterial group comprising archaea and eukaryota was called Neomura by Thomas Cavalier-Smith in 2002. However, in a cladistic view, Eukaryota are Archaea in the same sense as birds are dinosaurs because they evolved from the Maniraptora dinosaur group. In contrast, archaea without eukaryota appear to be
473-659: A nucleus. Both eukaryotes and prokaryotes contain large RNA / protein structures called ribosomes , which produce protein , but the ribosomes of prokaryotes are smaller than those of eukaryotes. Mitochondria and chloroplasts , two organelles found in many eukaryotic cells, contain ribosomes similar in size and makeup to those found in prokaryotes. This is one of many pieces of evidence that mitochondria and chloroplasts are descended from free-living bacteria. The endosymbiotic theory holds that early eukaryotic cells took in primitive prokaryotic cells by phagocytosis and adapted themselves to incorporate their structures, leading to
SECTION 10
#1732786846000516-414: A process that likely involves homologous recombination . These observations suggest that human MRE11 is descended from prokaryotic and protist ancestral Mre11 proteins that served a role in early processes for repairing DNA damage. MRE11 has a role in microhomology-mediated end joining (MMEJ) repair of double strand breaks. It is one of 6 enzymes required for this error prone DNA repair pathway. MRE11
559-690: A similar group of selfish individuals (see inclusive fitness and Hamilton's rule ). Should these instances of prokaryotic sociality prove to be the rule rather than the exception, it would have serious implications for the way we view prokaryotes in general, and the way we deal with them in medicine. Bacterial biofilms may be 100 times more resistant to antibiotics than free-living unicells and may be nearly impossible to remove from surfaces once they have colonized them. Other aspects of bacterial cooperation—such as bacterial conjugation and quorum-sensing-mediated pathogenicity , present additional challenges to researchers and medical professionals seeking to treat
602-473: A single founder (in the way that animals and plants are founded by single cells), which presents a number of theoretical issues. Most explanations of co-operation and the evolution of multicellularity have focused on high relatedness between members of a group (or colony, or whole organism). If a copy of a gene is present in all members of a group, behaviors that promote cooperation between members may permit those members to have (on average) greater fitness than
645-679: A stabilizing polymer matrix ("slime"), they may be called " biofilms ". Cells in biofilms often show distinct patterns of gene expression (phenotypic differentiation) in time and space. Also, as with multicellular eukaryotes, these changes in expression often appear to result from cell-to-cell signaling , a phenomenon known as quorum sensing . Biofilms may be highly heterogeneous and structurally complex and may attach to solid surfaces, or exist at liquid-air interfaces, or potentially even liquid-liquid interfaces. Bacterial biofilms are often made up of microcolonies (approximately dome-shaped masses of bacteria and matrix) separated by "voids" through which
688-435: A third domain: Eukaryota . Prokaryotes evolved before eukaryotes, and lack nuclei, mitochondria , and most of the other distinct organelles that characterize the eukaryotic cell. It was once thought that prokaryotic cellular components were unenclosed within the cytoplasm except for an outer cell membrane , but bacterial microcompartments , which are thought to be quasi-organelles enclosed in protein shells (such as
731-404: Is evidence on Mars of fossil or living prokaryotes. However, this possibility remains the subject of considerable debate and skepticism. The division between prokaryotes and eukaryotes is usually considered the most important distinction or difference among organisms. The distinction is that eukaryotic cells have a "true" nucleus containing their DNA , whereas prokaryotic cells do not have
774-671: Is a single-cell organism whose cell lacks a nucleus and other membrane -bound organelles . The word prokaryote comes from the Ancient Greek πρό ( pró ), meaning 'before', and κάρυον ( káruon ), meaning 'nut' or 'kernel'. In the two-empire system arising from the work of Édouard Chatton , prokaryotes were classified within the empire Prokaryota . However in the three-domain system , based upon molecular analysis , prokaryotes are divided into two domains : Bacteria (formerly Eubacteria) and Archaea (formerly Archaebacteria). Organisms with nuclei are placed in
817-486: Is an enzyme that in humans is encoded by the MRE11 gene. The gene has been designated MRE11A to distinguish it from the pseudogene MRE11B that is nowadays named MRE11P1 . This gene encodes a nuclear protein involved in homologous recombination , telomere length maintenance, and DNA double-strand break repair. By itself, the protein has 3' to 5' exonuclease activity and endonuclease activity. The protein forms
860-611: Is over-expressed in breast cancers. Cancers are very often deficient in expression of one or more DNA repair genes, but over-expression of a DNA repair gene is less usual in cancer. For instance, at least 36 DNA repair enzymes, when mutationally defective in germ line cells, cause increased risk of cancer (hereditary cancer syndromes ). (Also see DNA repair-deficiency disorder .) Similarly, at least 12 DNA repair genes have frequently been found to be epigenetically repressed in one or more cancers. (See also Epigenetically reduced DNA repair and cancer .) Ordinarily, deficient expression of
903-555: The encapsulin protein cages ), have been discovered, along with other prokaryotic organelles . While being unicellular, some prokaryotes, such as cyanobacteria , may form colonies held together by biofilms , and large colonies can create multilayered microbial mats . Others, such as myxobacteria , have multicellular stages in their life cycles . Prokaryotes are asexual , reproducing via binary fission without any fusion of gametes , although horizontal gene transfer may take place. Molecular studies have provided insight into
SECTION 20
#1732786846000946-503: The prokaryote archaeon Sulfolobus acidocaldarius . In this organism the Mre11 protein interacts with the Rad50 protein and appears to have an active role in the repair of DNA damages experimentally introduced by gamma radiation. Similarly, during meiosis in the eukaryotic protist Tetrahymena Mre11 is required for repair of DNA damages, in this case double-strand breaks , by
989-608: The archaea/eukaryote nucleus group. The last common antecessor of all life (called LUCA , l ast u niversal c ommon a ncestor) should have possessed an early version of this protein complex. As ATP synthase is obligate membrane bound, this supports the assumption that LUCA was a cellular organism. The RNA world hypothesis might clarify this scenario, as LUCA might have been a ribocyte (also called ribocell) lacking DNA, but with an RNA genome built by ribosomes as primordial self-replicating entities . A Peptide-RNA world (also called RNP world) hypothesis has been proposed based on
1032-478: The associated diseases. Prokaryotes have diversified greatly throughout their long existence. The metabolism of prokaryotes is far more varied than that of eukaryotes, leading to many highly distinct prokaryotic types. For example, in addition to using photosynthesis or organic compounds for energy, as eukaryotes do, prokaryotes may obtain energy from inorganic compounds such as hydrogen sulfide . This enables prokaryotes to thrive in harsh environments as cold as
1075-450: The bacterial phylum Planctomycetota has a membrane around the nucleoid and contains other membrane-bound cellular structures. However, further investigation revealed that Planctomycetota cells are not compartmentalized or nucleated and, like other bacterial membrane systems, are interconnected. Prokaryotic cells are usually much smaller than eukaryotic cells. Therefore, prokaryotes have a larger surface-area-to-volume ratio , giving them
1118-421: The biofilm—has led some to speculate that this may constitute a circulatory system and many researchers have started calling prokaryotic communities multicellular (for example ). Differential cell expression, collective behavior, signaling, programmed cell death , and (in some cases) discrete biological dispersal events all seem to point in this direction. However, these colonies are seldom if ever founded by
1161-495: The bodies of other organisms, including humans. Prokaryotes have high populations in the soil - including the rhizosphere and rhizosheath . Soil prokaryotes are still heavily undercharacterized despite their easy proximity to humans and their tremendous economic importance to agriculture . In 1977, Carl Woese proposed dividing prokaryotes into the Bacteria and Archaea (originally Eubacteria and Archaebacteria) because of
1204-454: The current set of prokaryotic species may have evolved from more complex eukaryotic ancestors through a process of simplification. Others have argued that the three domains of life arose simultaneously, from a set of varied cells that formed a single gene pool. This controversy was summarized in 2005: There is no consensus among biologists concerning the position of the eukaryotes in the overall scheme of cell evolution. Current opinions on
1247-530: The evolution and interrelationships of the three domains of life. The division between prokaryotes and eukaryotes reflects the existence of two very different levels of cellular organization; only eukaryotic cells have an enveloped nucleus that contains its chromosomal DNA , and other characteristic membrane-bound organelles including mitochondria. Distinctive types of prokaryotes include extremophiles and methanogens ; these are common in some extreme environments. The distinction between prokaryotes and eukaryotes
1290-484: The formation of the Earth's crust. Eukaryotes only appear in the fossil record later, and may have formed from endosymbiosis of multiple prokaryote ancestors. The oldest known fossil eukaryotes are about 1.7 billion years old. However, some genetic evidence suggests eukaryotes appeared as early as 3 billion years ago. While Earth is the only place in the universe where life is known to exist, some have suggested that there
1333-909: The four basic shapes of bacteria are: The archaeon Haloquadratum has flat square-shaped cells. Bacteria and archaea reproduce through asexual reproduction, usually by binary fission . Genetic exchange and recombination still occur, but this is a form of horizontal gene transfer and is not a replicative process, simply involving the transference of DNA between two cells, as in bacterial conjugation . DNA transfer between prokaryotic cells occurs in bacteria and archaea, although it has been mainly studied in bacteria. In bacteria, gene transfer occurs by three processes. These are (1) bacterial virus ( bacteriophage )-mediated transduction , (2) plasmid -mediated conjugation , and (3) natural transformation . Transduction of bacterial genes by bacteriophage appears to reflect an occasional error during intracellular assembly of virus particles, rather than an adaptation of
Mre11 - Misplaced Pages Continue
1376-432: The host bacteria. The transfer of bacterial DNA is under the control of the bacteriophage's genes rather than bacterial genes. Conjugation in the well-studied E. coli system is controlled by plasmid genes, and is an adaptation for distributing copies of a plasmid from one bacterial host to another. Infrequently during this process, a plasmid may integrate into the host bacterial chromosome, and subsequently transfer part of
1419-537: The host bacterial DNA to another bacterium. Plasmid mediated transfer of host bacterial DNA (conjugation) also appears to be an accidental process rather than a bacterial adaptation. Natural bacterial transformation involves the transfer of DNA from one bacterium to another through the intervening medium. Unlike transduction and conjugation, transformation is clearly a bacterial adaptation for DNA transfer, because it depends on numerous bacterial gene products that specifically interact to perform this complex process. For
1462-426: The idea that oligopeptides may have been built together with primordial nucleic acids at the same time, which also supports the concept of a ribocyte as LUCA. The feature of DNA as the material base of the genome might have then been adopted separately in bacteria and in archaea (and later eukaryote nuclei), presumably by help of some viruses (possibly retroviruses as they could reverse transcribe RNA to DNA). As
1505-692: The intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=Mre11&oldid=1132082502 " Category : Disambiguation pages Hidden categories: Short description is different from Wikidata All article disambiguation pages All disambiguation pages MRE11A 4361 17535 ENSG00000020922 ENSMUSG00000031928 P49959 Q61216 NM_005590 NM_005591 NM_001330347 NM_018736 NM_001310728 NP_001317276 NP_005581 NP_005582 NP_001297657 NP_061206 Double-strand break repair protein MRE11 ( Meiotic recombination 11 )
1548-424: The major differences in the structure and genetics between the two groups of organisms. Archaea were originally thought to be extremophiles, living only in inhospitable conditions such as extremes of temperature , pH , and radiation but have since been found in all types of habitats . The resulting arrangement of Eukaryota (also called "Eucarya"), Bacteria, and Archaea is called the three-domain system , replacing
1591-406: The medium (e.g., water) may flow easily. The microcolonies may join together above the substratum to form a continuous layer, closing the network of channels separating microcolonies. This structural complexity—combined with observations that oxygen limitation (a ubiquitous challenge for anything growing in size beyond the scale of diffusion) is at least partially eased by movement of medium throughout
1634-571: The mitochondria and chloroplasts. The genome in a prokaryote is held within a DNA/protein complex in the cytosol called the nucleoid , which lacks a nuclear envelope . The complex contains a single, cyclic, double-stranded molecule of stable chromosomal DNA, in contrast to the multiple linear, compact, highly organized chromosomes found in eukaryotic cells. In addition, many important genes of prokaryotes are stored in separate circular DNA structures called plasmids . Like eukaryotes, prokaryotes may partially duplicate genetic material, and can have
1677-403: The nucleus, that eukaryotes arose without endosymbiosis, and that eukaryotes arose through a symbiotic event entailing a simultaneous endosymbiotic origin of the flagellum and the nucleus, in addition to many other models, which have been reviewed and summarized elsewhere. The oldest known fossilized prokaryotes were laid down approximately 3.5 billion years ago, only about 1 billion years after
1720-408: The origin and position of eukaryotes span a broad spectrum including the views that eukaryotes arose first in evolution and that prokaryotes descend from them, that eukaryotes arose contemporaneously with eubacteria and archaebacteria and hence represent a primary line of descent of equal age and rank as the prokaryotes, that eukaryotes arose through a symbiotic event entailing an endosymbiotic origin of
1763-427: The snow surface of Antarctica , studied in cryobiology , or as hot as undersea hydrothermal vents and land-based hot springs . Prokaryotes live in nearly all environments on Earth. Some archaea and bacteria are extremophiles , thriving in harsh conditions, such as high temperatures ( thermophiles ) or high salinity ( halophiles ). Many archaea grow as plankton in the oceans. Symbiotic prokaryotes live in or on
Mre11 - Misplaced Pages Continue
1806-426: The traditional two-empire system . According to the phylogenetic analysis of Hug (2016), the relationships could be the following: A widespread current model of the evolution of the first living organisms is that these were some form of prokaryotes, which may have evolved out of protocells , while the eukaryotes evolved later in the history of life. Some authors have questioned this conclusion, arguing that
1849-520: Was firmly established by the microbiologists Roger Stanier and C. B. van Niel in their 1962 paper The concept of a bacterium (though spelled procaryote and eucaryote there). That paper cites Édouard Chatton 's 1937 book Titres et Travaux Scientifiques for using those terms and recognizing the distinction. One reason for this classification was so that what was then often called blue-green algae (now called cyanobacteria ) would not be classified as plants but grouped with bacteria. Prokaryotes have
#0