Mitochondria

ID #2443

Which RNA polymerases function in the lumen of the human nmitochindrion and why can we only expect for there to be one? Why is this RNA polymerase not coded by a mitochondrial genome? Is it because all RNA polymerases in the cell are consistent, hence all coded for by the same gene?


The mitochondrion has its own replication, transcription and translation systems that all occur in the mitochondrial matrix. It has its own RNA polymerase, which is encoded in the nucleus. (Since bacteria only have one RNA polymerase, it makes sense that mitochondria only have one as well). Because a mitochondrion resembles a bacterial cell more closely than a eukaryote, it is likely that a eukaryotic RNA polymerase would be unable to recognize "bacterial-like" promoters. 
Remember, according to the endosymbiont theory, mitochondria were once free living organisms that did all of their own replication, transcription, and translation. Though they have moved some of their genes to the nucleus over time to better focus on generating energy, they still carry out some of those processes more like their bacterial ancestors than like their eukaryotic hosts. 
I am not sure what you mean about all RNA polymerases being consistent - remember, in eukaryotes there is RNA polymerase I, RNA Pol II, and RNA pol III depending on what type of RNA is being transcribed. 

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