Mitochondria: origin

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According to this hypothesis (Margulis, 1993), the eukaryotic cell is a result of symbiosis of different prokaryotic cells, where mitochondria originated from eubacteria, and chloroplasts - from cyanobacteria, and vacuoles - from archae. 

Figure 9 Predicted structures of ribosomal RNA from (a) the archaeon Halo-bacterium volcanii, (b) the eukaryote baker s yeast, and (c) cow mitochondria. RNA is single-stranded, but, as in DNA, the letters can pair up to form bridges between two chains. In the case of RNA, a single chain doubles back on itself to form loops and hairpins (whereas the famous DNA double helix is in fact two distinct chains entwined in a helix). The bubbles in this illustration are single-stranded RNA, in which the letters have not paired up. A comparison of the three ribosomal RNAs shows that the overall shape and structure of ribosomal RNA (its secondary structure) has been maintained throughout evolution. However, the actual sequence of letters has drifted substantially, and the sequence similarities are very low. The mitochondrial RNA structure is reminiscent of bacterial RNA, from which the mitochondria originated. Adapted with permission from Gutell et al.t and Progress in Nucleic Acid Research and Molecular Biology.

Given their ubiquitous distribution, the PRAT Tims may have had an early origin during the conversion of the proto-mitochondrion. However, these putative translocases have yet to be localized, and no phylogenetic analyses have been generated to assess their affinities. 

Because Rlil homologs have been found only in archaebacteria (reviewed in Tachezy and Dolezal 2007), it is hypothesized that Rlil and other components of cytosolic translation machinery are derived from them. Therefore, we propose that the intimate association of the relic mitochondrion, of eubacterial origin, with its associated membranes is a structural reflection of the cell s attempt to facilitate efficient ribosome biogenesis and translation initiation following reductive evolution of the organelle (Keeling 2004 ... 

The compartmentalization of energy generation provides a mechanism for the increased efficiency of high energy bond transfer to form the ultimate cellular fuel ATP, and has been the driving force behind the evolution of the mitochondrion. This viewpoint is supported by studies of the mitochondrial proteome, which have demonstrated that proteins of eubacterial origin predominantly... 

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The acetyl-CoA used as substrate for fatty acid synthases in the cytosol originates from the mitochondrion. This acetyl-CoA condenses with C02 to form malonyl-CoA, which eliminates (XL after an initial condensation reaction. After three more steps a two-carbon unit is added to a growing fatty acid chain. This cycle repeats itself many... 

Therefore, as a mitochondrion membrane is broken, it somewhat disrupts communications between two conjugated reactions (respiration and phosphorylation). Hence, as expected, phosphorylation is completely terminated. This kinetic behavior of the system, both unclear and unusual at first glance, is quite logical, and is associated with the membrane origin of the ATP synthesis. 

Oxidative phosphorylation is ATP synthesis linked to the oxidation of NADH and FADH2 by electron transport through the respiratory chain. This occurs via a mechanism originally proposed as the chemiosmotic hypothesis. Energy liberated by electron transport is used to pump H+ ions out of the mitochondrion to create an electrochemical proton (H+) gradient. The protons flow back into the mitochondrion through the ATP synthase located in the inner mitochondrial membrane, and this drives ATP synthesis. Approximately three ATP molecules are synthesized per NADH oxidized and approximately two ATPs are synthesized per FADH2 oxidized. 

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