xyzbbruner at uclink4.berkeley.edu
Mon Oct 13 20:00:56 EST 2003
On Sun, 12 Oct 2003 16:54:25 +0200, CyberLegend aka Jure Sah
<jure.sah at guest.arnes.si> wrote:
>Tom Anderson wrote:
>> On Thu, 2 Oct 2003, CyberLegend aka Jure Sah wrote:
>> > I have heard such that the organels have evolved seperately and were
>> > eventualy 'absorbed' into the cells and continued to live there.
>Yes indeed I did notice the genome inside of those as well, but it is
>equaly hard to explain why a standalone cell (a standalone mitochondrion
>for example) would have the function it has.
Not at all. The key function that the mito provides is the fundamental
reaction set of oxidative metabolism, which fuels many bacteria. That
is, the free living organism was an aerobic bacterium. It was
ingested, and over time it degenerated -- leaving the key oxidative
functions, and only a tiny genome.
There is actually enough info about mito details to allow a pretty
good guess as to which specific kind of bacteria served as the
>Also given that the outer
>membrane of the mitochondrion is of the cell that absorbed them, it
>would be hard to imagine a natural environment loaded with H+ ions for
>the standalone mitochondrion to use.
That is all subsumed by the fist point, that this is normal metabolism
for the precursor bacteria.
>My idea of it is that eukaryotic cells had, like procaryonts,
>free-floating circular DNA strands (procaryontic plasmids) that in their
>time took care of the synthesys of ATP around the cell, which had
>eventualy evolved into mitochondrion.
You have to deal with the fact that free DNA is quite unstable in
modern eukaryotic cytoplasm, and does not replicate. Even if you
finesse that point, can you provide any evidence for such a model, in
the face of considerable (overwhelming?) evidence for endosymbiosis.
I suspect that the amount of genome required for such a plasmid (in
its original form) is quite large!
>I guess the test would be to take a mitochondrion out of a cell and see
>if it can survive and replicate.
It is not possible, but would prove nothing even if it were. The mito
are much too degenerate to grow on their own. Alone, that does not say
what they degenerated from.
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