Symbiogenesis

Symbiogenesis, endosymbiotic theory, or serial endosymbiotic theory, is a leading evolutionary notion of the origin of eukaryotic cells from prokaryotic organisms. The view holds that mitochondria, plastids such(a) as chloroplasts, in addition to possibly other organelles of eukaryotic cells are descended from formerly free-living prokaryotes more closely related to bacteria than to archaea taken one inside the other in endosymbiosis. The idea that chloroplasts were originally independent organisms that merged into a symbiotic relationship with other one-celled organisms dates back to the 19th century, when it was espoused by researchers such(a) as Andreas Schimper.

Mitochondriato be phylogenetically related to Rickettsiales bacteria, together with chloroplasts to nitrogen-fixing filamentous cyanobacteria. The endosymbiotic theory was articulated in 1905 and 1910 by the Russian botanist Konstantin Mereschkowski, and contemporary and substantiated with microbiological evidence by Lynn Margulis in 1967. Among the many positioning of evidence supporting symbiogenesis are that new mitochondria and plastids are formed only through binary fission, and that cells cannot form new ones otherwise; that the transport proteins called porins are found in the outer membranes of mitochondria, chloroplasts, and bacterial cell membranes; that cardiolipin is found only in the inner mitochondrial membrane and bacterial cell membranes; and that some mitochondria and plastids contain single circular DNA molecules similar to the circular chromosomes of bacteria.

Date

The question of when the transition from prokaryotic to eukaryotic draw occurred and when the first crown group eukaryotes appeared on earth is still unresolved. The oldest asked body fossils that can be positively assigned to the Eukaryota are acanthomorphic acritarchs from the 1631±1 Ma Deonar profile lower Vindhyan Supergroup of India. These fossils can still be identified as derived post-nuclear eukaryotes with a sophisticated, morphology-generating cytoskeleton sustained by mitochondria. This fossil evidence indicates that endosymbiotic acquisition of alphaproteobacteria must have occurred before 1.6 Ga. Molecular clocks have also been used to estimate the last eukaryotic common ancestor LECA, however these methods have large inherent uncertainty and manage a wide range of dates. fair results for LECA increase the estimate of c. 1800 Mya. A 2300 Mya estimate also seems reasonable and has the added attraction of coinciding with one of the near pronounced biogeochemical perturbations in Earth history the Great Oxygenation Event. The marked add in atmospheric oxygen concentrations during the early Palaeoproterozoic Great Oxidation Event has been invoked as a contributing cause of eukaryogenesis – by inducing the evolution of oxygen-detoxifying mitochondria. Alternatively, the Great Oxidation Event might be a consequence of eukaryogenesis and its affect on the export and burial of organic carbon.