LYAGER.HIDE@BIONET-20.BIO.NET (Winston Hide) (10/26/88)
I would appreciate anyone's views on the origin of mitochondria: In particular? is it accepted that their origin is monophyletic or is it polyphyletic? I am aware of the symbiotic story, however, I would really like to know if I were faced with a question where I saw waht looked like a bacterium inside a cell(both old ) How would I test for the bacterium-like organelle being a mtiochondrion? What definitive gene could I probe for? I aplogise for my naivete, but the answer to the question is important to me at this time. I look forward to hereing from someone, or atleast being pointed in the right direction Thankyou. Win Hide Temple University. -------
kramerj@bionette.CS.ORST.EDU (Jack Kramer - CMBL) (10/27/88)
The origin is still controversial although the work of Lynn Margolis has swayed most to the serial symbiotic hypothesis. In this theory the proto eukaryote progressed to an organism somewhat similar to present day eukaryotes but lacked mitochondria and plastids. These organelles were acquired by by fortuitous persistent invasion by protomitochondria and protoplastids, which progressed from obligate endo cellular symbionts to organelles. If you start tracing the literature with Lynn's name you will find probably much more literature on this than you will want to persue. I have my own differing theory which can probably be considered way out in left field. I call it the coalescent theory. It goes like this. Prokaryotes populated the earth for approximately 2 billion years before the appearance of anything which we would call a eukaryote. During this time many symbiotic associations, parasitic, mutual, and commensal, were formed. One of the primary obligate commensal associations is the same as the major biological association in the current world; that is the cyclicly dependent photosynthesis/resriration association. Proto- mitochondria and protoplastids formed increasingly obligate communal organisms. These may at this time still have had an RNA based genome with its many limitations. But independently the DNA based prokariote evolved and being so much more accurate in its genetic control mechanism that when it became associated with the mitoplastid colony it took over the master genetic control functions. The new colonies were even more successful and prolifferated. Similarly, the motile prokaryotes joined in with some of the colonies. This differs form the serial symbiosis theory in that up to this stage all the elements are still independent prokariotes joined into colonies. Since there were many different kinds of plastids (red, green, yellow-green, golden, etc.) which are still represented in the many parallel line of existing algae, these lineages may have been independent before the origin of the eukaryote. Thus the many morphologically similar lines of organisms which differ ultrastructurally are really convergent groups which evolved in parallel from the many combinations of prokaryotic colonies. These colonies, through increasingly obligate association formed an enveloping shell to control the immediate environment and provide protection. The most successful of these colonial lineages became eukariotes. This is the only theory which fits all thermodynamic, geological, and biological evidence that I am familiar with. I don't talk about it much any more since all my experimental approaches to date have failed to provide proof that any of the potential "missing link" organisms would fit the theory. I got tired of being told to go to the library and just look up the way we already know it happened. If I could only find a way to get the @#%**@$#& nuclear ribosomal RNA out of Nanochlorum eukaryotum I feel that this may change. Jack Kramer Computational Molecular Biology Laboratory Oregon State University