Life before and during the primitive endosymbiosis. Dissemination 65th
The endosymbiosis hypothesis suggests that early free prokaryotes were mitochondria for several reasons:
(a) Not all eukaryotes have chloroplasts
(b) Mitochondria have their own DNA
(c) Mitochondria only come from other mitochondria
(d) The prokaryotic ribosomes are similar to mitochondrial ribosomal
This approach endosymbiosis hypothesis implies the existence of several "actors" prior to the formation of eukaryotes but does not explain which are the origins of these actors and therefore seems difficult to correspond with reality. Thus, according to endosymbiosis hypothesis, through a process of serial endosymbiosis, the ancestral eukaryotic cell acquired an endosymbiont capable of photosynthesis (cyanobacteria) that later would lead to algae. In addition to this difficulty, the current hypothesis of endosymbiosis has two major shortcomings:
(*) "Mitochondria can not survive in an environment free of oxidizable organic carbon" Without free oxygen without organic matter only can survive chloroplasts which produce both from CO2 and solar energy.
(*) "The chloroplasts synthesize ATP by photophosphorylation, inorganic phosphate that is coupled to ADP to form ATP comes from own photons of sunlight, on the other hand mitochondria release ATP by oxidative phosphorylation "Without ATP can only survive chloroplasts.
Therefore there are other simpler and comprehensive approaches, accepting the basic idea of endosymbiosis, in our opinion, these give a better explanation of the beginning of the process from a single base molecule: circular chloroplast DNA.
(1) A circular DNA molecule of chloroplasts has the ability to produce their own ribosomes and their own cell wall, in a medium rich in amino acids, originating the first prokaryotic (pro plastid) capable of feeding producing their own organic matter (rbc S genes, L, M read bidirectionally).
(2) This pro plastid is able to reproduce by duplication its circular DNA and posterior membrane bipartition. This phenomenon could have developed some 3,800 million years ago (Precambrian eoarchaic) as evidenced by the fossil chemical rests, the shift C13/C12 percentages, greater than 89 mineral carbonates, on D'Isua and Warrawoona that allow to know the existence of a process of elaboration of organic carbon. At this time the concentration of O2 in the atmosphere would be 0.075%.
(3) This pro-plastid could also result in another being prokaryotic for lost of part of its genetic material, keeping the unidirectional reading rbc genes, while maintaining the new circular DNA molecule structure. Thus a second free prokaryotic called mitochondria that would equal the original capabilities proplasto except the synthesis of organic material from the sun's energy. This process could have evolved about 3,100 million years ago (Precambrian Mesoarchean) as evidenced by the existence of iron oxide sediment, which implies the existence of sufficient free oxygen to be used in the production of energy from the organic matter produced in the preceding 700 million years. At this time the concentration of free O2 in the atmosphere would be 0.12%.
(4) From this moment prokaryotes can evolve into eukaryotes by endosymbiosis several options:
4.1 The division of a pro-plastid brings the inclusion of brother into another resulting in a eukaryotic plant by a process which we may call self – endosymbiosis or "ipsum-endo-symbiosis"
4.2 The division of a mitochondrion causes the brother inclusion inside of itself resulting on an eukaryotic animal.
In both cases would be released circular DNA without membrane that could be the origin of the eukaryotic cell nucleolus molecule.
(5) Processes of multiple endosymbiosis have occurred later, as evidenced by some of today's eukaryotic plastids have up to 3 or 4 membranes around. This would explain the formation of current eukaryotes: multiple endosymbiosis and subsequent natural selection of the most efficient models in terms of reproductive capacity and adaptation to environmental changes (the formation of the protective layer, to sunlight, ozone is initiated when the concentration of O2 in the atmosphere above the 1% while the current concentration of O2 in the atmosphere is 20%).
This second approach can explain the presence of mitochondria and chloroplasts in eukaryotic cell differentiation in tissues in multicellular beings and linking dependence animal eukaryotic cells have regarding plant eukaryotic cells.