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Sunday, April 23, 2017

Organellogenesis


With the traditional theory all organelles were created locally, by a process called "organellogenesis". The endosymbiosis process introduced an alternative way by which organelles could have been created. For two of the organelles, mitochondria and chloroplasts, the process of endosymbiosis has been used as an explanation for similarities of these to free living bacteria. All these endosymbiosis processes are assumed to have been performed only once, maybe with the exception of chloroplast genesis, which by several theories have been performed twice. And all these processes are assumed to have been completed more than a billion years ago. 

The internal incidents of organogenesis may have been slow, iterative processes, but the endosymbiosis events must have been completed in very short time. That includes not only the establishment of a dependency relation between the intruding bacterium and its host, but also the transfer of genes to the nucleus. That is documented by the introns that are assumed to have been inserted in the genes. They are found on the same places in organisms that are only distantly related.

But organellogenesis takes place also today. REF (small things ) describes an incidence?? of endosymbiosis that has taken place within the last ??? years. In light of the posited PÅSTÅTTE improbability of endosymbiosis (REF Lane) this is a sensation. If this is an endosymbiosis following the evolution trends of the ancient cases, then we should expect to see massive transfer of genes to the nucleus. But that is not reported (??). 

And this is not the only case of organellogenesis reported. In REF NAVN reports the discovery of 18? cases of endosymbiosis, where an organelle has been exchanged (?) with a new bacterium. (SJEKK) Also here there is no finding of massive transfer of genes to the nucleus. This is as far from the evolutionary endosymbiosis at it is possible to come. But such cases have been used as proof for endosymbiosis. It is evident that these organelles have not been created locally independently of the bacteria that surround them. In fact their genomes are in all cases related to local bacteria. But that is not equivalent to origin by endosymbiosis. 

With OET((REF)) new organelle variants with relation to surrounding bacteria may occur in two ways: either by bacteria becoming organelles or by organelles becoming bacteria. In this case a much simpler explanation is that these organelles have originated in their ancient hosts, have evolved to become partly stationary and partly commuting, and the commuting variant would be classified as bacteria. 

It is evident that the commuting organelles that surround the host are related to the stationary variant of the organelle, as they have a common source of genes. In these cases the stationary variant is very autonomous. They are really just temporarily stationary. Either they are equipped from their host with genes to become commuting or they are really competing with variants that are commuting. The best way to regard them is probably as a part of a common community. By chance some variants become stationary for a period before they are outcompeted by others in the community. We could use the term organellogenesis for all these cases, but it is really part of a continuous process, where some commuting organelles become dependent of their host due to loss of some gene. I would not call this endosymbiosis, as the relation between host and guest is present all the time.

The big difference is that mitochondria and chloroplasts are B organelles ((REF. quora OET)) (eubacteria when autonomous), which are basically electron acceptors (or the opposite), while the modern organelles are A organelles (archaebacteria when autonomous). The latter are basically hydrogen consumers. The B organelles are naturally stationary when the final electron acceptor/donor is a neutral molecule. The A organelles however always thrive well outside their host, and are used as stationary mainly as a complement to a B organelle hydrogenosome. 

For an alternative explanation of the origin of e.g. mitochondria, refer to the evolution of metabolism in OET or to OET generally.  

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