tag:blogger.com,1999:blog-37148773.post6679780442256504763..comments2024-03-18T09:58:09.828-04:00Comments on <center>Sandwalk</center>: Better Biochemistry: The Problem with Glycerol Phosphate and Citrate and What This Has to Do with Archaebacterial MembranesLarry Moranhttp://www.blogger.com/profile/05756598746605455848noreply@blogger.comBlogger6125tag:blogger.com,1999:blog-37148773.post-85106801893531650272011-11-28T18:11:09.052-05:002011-11-28T18:11:09.052-05:00@Anon
I think you are splitting taxonomic hairs. ...@Anon<br /><br />I think you are splitting taxonomic hairs. There is so much gene transfer involved in these groups in any case ... I was initially referring to the membrane system only, and following the common convention of calling the one "archaeal" and the other "bacterial". Yes, the common ancestor of bacteria and archaea was neither bacterium nor archaeon. And we can't call it an archaebacterium either; that's taken. Call it what the heck you like. As far as its membranes are concerned:<br /><br />1) It had none <br />2) It had the "archaeal" arrangement. <br />3) It had the "bacterial" (and now eukaryote) arrangement<br />4) It had some other membrane architecture.<br /><br />My original point was to reject 1). <br /><br />As to whether the bacterial or archaeal arrangement is more plausibly ancestral out of 2) and 3), I would still plump for 2) on the grounds that this is more stable in high-temperature environments. If life did not originate in such environments, then I'm wrong. But selection would favour a move to 3) as 'true' bacteria and archaea split. Endosymbiosis involved a fusion either of systems 2) and 3), or 3) and 3). In the former case. sole retention of 3) would be favoured during the cementing of the endosymbiotic union, since we are low-temperature organisms.<br /><br /><i>Another portion of the population evolved and gave rise to eukaryotes, a population that evolved a symbiotic relationship with a certain set of bacteria.</i> <br /><br />Myself, I favour the view that eukaryotes only arose on endosymbiosis.Allan Millernoreply@blogger.comtag:blogger.com,1999:blog-37148773.post-79897709050572959022011-11-28T13:42:56.851-05:002011-11-28T13:42:56.851-05:00The common ancestor of humans and chimps was most ...<i> The common ancestor of humans and chimps was most likely not a chimp nor a human.</i><br /><br />But it was clearly a primate.<br /><br />True - we do not know if the ancestor would have been placed within the modern taxonomic grouping of "archaeon" organisms. But there are some who hold that eukaryotes group within achaeon (not sister to). Others do not. Calling the other camp "wrong" at this point is a bit premature.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-37148773.post-50121676575299250262011-11-28T11:05:14.873-05:002011-11-28T11:05:14.873-05:00My point was that it is well established that we d...My point was that it is well established that we derive from an endosymbiotic event between an archaeon and a bacterium. <br />**********************<br />My point is that you are incorrect. It is not a well established. Eukaryotes do share a common ancestor with archaea in many regards. That ancestral population was not an archaeon. Part of that population evolved and gave rise to archaea. Another portion of the population evolved and gave rise to eukaryotes, a population that evolved a symbiotic relationship with a certain set of bacteria. The common ancestor of humans and chimps was most likely not a chimp nor a human.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-37148773.post-81423032089361689142011-11-27T13:56:08.029-05:002011-11-27T13:56:08.029-05:00Derive from archaea? For many traits we share a co...<i>Derive from archaea? For many traits we share a common ancestor with archaea but that doesn't make that common ancestor an archaeon.<br /><br />Why assume archaea have the more ancestral form? They are modern organisms like humans, E. coli, etc.</i><br /><br />My point was that it is well established that we derive from an endosymbiotic event between an archaeon and a bacterium. The bacterium became our mitochondria, and the archaeon gave us much of the rest of the cell. Except the membranes. Forget ancestry; if it was an archaeon, it had archaeal membranes, and we don't.Allan Millernoreply@blogger.comtag:blogger.com,1999:blog-37148773.post-6060803649377083022011-11-21T10:30:45.781-05:002011-11-21T10:30:45.781-05:00Derive from archaea? For many traits we share a c...Derive from archaea? For many traits we share a common ancestor with archaea but that doesn't make that common ancestor an archaeon. <br /><br />Why assume archaea have the more ancestral form? They are modern organisms like humans, E. coli, etc.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-37148773.post-88414588870942891842011-11-18T05:12:40.108-05:002011-11-18T05:12:40.108-05:00It might even suggest that membranes and their lip...<i>It might even suggest that membranes and their lipids arose independently in the two lineages. To some, this means that lipids and membranes were late-comers in the evolution of life (e.g. Koonin, 2012).</i><br /><br />Given that our cells mostly derive from archaea, but our membranes from bacteria (presumably from the mitochondrion), I'd say that it's more likely that one membrane architecture can simply supplant another. If (for example) the archaeal membrane were the more ancient, and a descendant lineage started producing a few molecules of the bacterial lipid arrangement, one could envisage a growing 'patch' of bacterial membrane that became the sole resident. When, on endosymbiotic union, those two systems again encountered each other, again the bacterial system won. Pure speculation, but I think the close involvement of membranes with energetics and other gradient processes argues against late arrival. Glycolysis is all very well, but...Allan Millernoreply@blogger.com