Endosymbiotic theory (endosymbiont hypothesis) This hypothesis because sufficient evidence has been accepted by more and more people. It's mainly based on: (1) symbiosis is a common biological phenomenon, such as Rhizobium symbiotic relationship with leguminous plants, algae or green algae to form lichen symbiosis with fungi and so on. There is a paramecium (paramoeciumbursaria), the body associated symbiotic algae and small, and can carry out photosynthesis; past the digestive tract of termites that live in Australia, a so-called mixed caterpillar (mixotricha paradoxa), actually consists of two spirochetes, two true composition of bacteria and a ciliate, they can secrete the enzyme, digestion of cellulose. Particularly in recent years, algal spores found in the ash (glancocystis), which itself has no chlorophyll, but there are many leaves blue bodies (cyanella) living in the body to carry out photosynthesis food. This symbiotic relationship seems to not be established for a long time, because the leaves of blue bodies in the cell is not big fixed. Gray spore algae found on the "endosymbiotic hypothesis" strong support. (2) chloroplasts and mitochondria has its own unique dna, free to copy, is not entirely under the control of nuclear dna. Mitochondria and chloroplast dna dna with the nucleus are very different, but with the dna of bacteria and cyanobacteria is very similar. Cyanobacterial ribosomal rna (rrna) not only own dna hybridization with cyanobacteria, but also with the Euglena chloroplast dna hybridization, these show homology between them. (3) mitochondria and chloroplasts have their own specific protein synthesis system from the control of nuclear synthesis system. Prokaryotic ribosomal 30s and 50s by the two subunits of eukaryotic ribosomal 40s and 60s by the two subunits. Mitochondria and chloroplast ribosomes of bacteria and cyanobacteria, respectively, consistent with, but also from the 30s and 50s two subunits, indicating that bacteria and mitochondria, cyanobacteria, and chloroplasts are homologous. Antibiotics can inhibit the growth of bacteria and cyanobacteria, but also can inhibit eukaryotes the role of mitochondria and chloroplasts, mitochondria and this also shows that bacteria, chloroplasts and cyanobacteria are homologous. (4) mitochondria, chloroplasts, the outer membrane were significantly different, within, between the outer membrane filled with liquid. Found that they, the outer membrane of the chemical composition is different. Outer membrane are consistent with the host membrane, and endoplasmic reticulum in particular, are very similar; endometrium with the bacteria and cyanobacteria were similar to the membrane. In short, "the endosymbiotic hypothesis" has been a wide range of experimental support, they have been accepted by more and more people. But it also has shortcomings, mainly: First, it did not say what the origin of the nucleus; second, it believed that after the spirochetes into the eukaryotic cells can form flagella, this view is clearly wrong, because the spiral is a prokaryotic biology, the flagellum is not "9 +2" structure, and eukaryotes such as Euglena Paramecium cilia or the flagellum is a "9 +2" structure. Spiral into the amoeba-shaped prokaryotic cells to form a "9 +2" structure of the flagellum, "the endosymbiotic theory" and did not give specific instructions.
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History
In 1905, Konstantin Mereschkowsky was first put forward from the original endosymbiotic chloroplast formation of the idea, followed by Ivan Wallin in the 1920s raised the idea on the same mitochondria. As people found that they contain DNA, these ideas were Henry Ris reintroduced. Endosymbiotic hypothesis was popularized by 琳马古利斯. In her 1981 "Symbiosis in Cell Evolution", she considered the origin of eukaryotic cells composed of individuals in the community interaction, including the spiral shape into endosymbiotic eukaryotic flagella and cilia. The latter idea was not widely accepted because of the lack of flagella DNA, outside of the structure and prokaryotes have no obvious similarities. According to Margulis and Sagan (1996), "Life is not through fighting, but take the whole world through collaboration", and Darwin on the evolution driven by the idea of competition is imperfect. However, it was more like slavery than that within the symbiotic mutualism. Some people think that peroxisomes may also have endosymbiotic origin, although they lack DNA. Christian de Duve that they may be the first endosymbionts, making the cells resistant to the Earth's atmosphere more and more oxygen. However, it now appears they may be "de novo", rather than a symbiotic origin.
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Evidence
内共生学说 证据
This hypothesis because sufficient evidence has been accepted by more and more people. It's mainly based on: (1) symbiosis is a common biological phenomenon, such as Rhizobium symbiotic relationship with leguminous plants, algae or green algae to form lichen symbiosis with fungi and so on. There is a paramecium (Paramoeciumbursaria), the body associated symbiotic algae and small, and can carry out photosynthesis; past the digestive tract of termites that live in Australia, a so-called mixed caterpillar (Mixotricha paradoxa), actually consists of two spirochetes, two true composition of bacteria and a ciliate, they can secrete the enzyme, digestion of cellulose. Particularly in recent years, algal spores found in the ash (Glancocystis), which itself has no chlorophyll, but there are many leaves blue bodies (cyanella) living in the body to carry out photosynthesis food. This symbiotic relationship seems to not be established for a long time, because the leaves of blue bodies in the cell is not big fixed. Gray spore algae found on the "endosymbiotic hypothesis" strong support. (2) chloroplasts and mitochondria has its own unique DNA, can be free to reproduce, not entirely under the control of nuclear DNA. Mitochondrial DNA and chloroplast DNA with the nucleus are very different, but with the DNA of bacteria and cyanobacteria are very similar. Cyanobacterial ribosomal RNA (rRNA) can not only DNA hybridization with the cyanobacteria itself, but also with the Euglena chloroplast DNA hybridization, this shows that the homology between them. (3) mitochondria and chloroplasts have their own specific protein synthesis system from the control of nuclear synthesis system. Prokaryotic 30S and 50S ribosomal subunits by the composition of eukaryotic 40S and 60S ribosomal subunits from the composition. Mitochondria and chloroplast ribosomes of bacteria and cyanobacteria, respectively, consistent with, but also by the two subunits 30S and 50S, indicating that bacteria and mitochondria, cyanobacteria, and chloroplasts are homologous. Antibiotics can inhibit the growth of bacteria and algae, can also inhibit the eukaryotic mitochondrial and chloroplast, and this also shows that bacteria and mitochondria, chloroplasts and cyanobacteria are homologous. (4) mitochondria, chloroplasts, the outer membrane were significantly different, within, between the outer membrane filled with liquid. Found that they, the outer membrane of the chemical composition is different. Outer membrane are consistent with the host membrane, and endoplasmic reticulum in particular, are very similar; endometrium with the bacteria and cyanobacteria were similar to the membrane. In short, "the endosymbiotic hypothesis" has been a wide range of experimental support, they have been accepted by more and more people. But it also has shortcomings, mainly: First, it did not say what the origin of the nucleus; second, it believed that after the spirochetes into the eukaryotic cells can form flagella, this view is clearly wrong, because the spiral is a prokaryotic biology, the flagellum is not "9 +2" structure, and eukaryotes such as Euglena Paramecium cilia or flagella are the "9 +2" structure. Spiral into the amoeba-shaped prokaryotic cells to form a "9 +2" structure of the flagellum, "the endosymbiotic theory" and did not give specific instructions.
