Cell creation

Hello everybody,

I'm looking for links to existant hypotesys' (and of course the
hypotesys' themselves) on how diffirent cell organels have evolved.

I have heard such that the organels have evolved seperately and were
eventualy 'absorbed' into the cells and continued to live there. I
wonder how many hypotesys' are there that support the claim that the
organels have evolved in the cells themselves?

Thanks in advance.

Observer aka DustWolf aka CyberLegend aka Jure Sah

C'ya!

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On Thu, 2 Oct 2003, CyberLegend aka Jure Sah wrote:


This theory is known as 'serial endosymbiosis', and it only applies to the
mitochondrion and the chloroplast; some people suggest that eukaryotic
cilia and flagella (aka undulipodia) are also derived from bacteria, but
that is much less widely believed.

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That's an interesting question. I don't think there are any current
hypotheses which explain the origin of the mitochondrion or chloroplast
without reference to endosymbiosis. The killer evidence is that those
organelles have their own genomes, which are more similar to bacterial
than eukaryotic genomes; it's hard to see how such genomes could have
developed inside a eukaryotic cell.

tom

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Tom Anderson, MRC Laboratory of Molecular Cell Biology, UCL
Disclaimer: I really have no idea what i'm talking about.

Tom Anderson wrote:

Thank you very much.


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. 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.

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.

I guess the test would be to take a mitochondrion out of a cell and see
if it can survive and replicate.

I'm also very interested how does the endosymbiosis theory explain the
existantce other (non chloroplast) plastids.

Observer aka DustWolf aka CyberLegend aka Jure Sah

C'ya!

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Cellphone: +38640809676 (SMS enabled)

Don't feel bad about asking/telling me anything, I will always gladly
reply.

"Yes, Master."

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On Sun, 12 Oct 2003 16:54:25 +0200, CyberLegend aka Jure Sah
<[Only registered users see links. ]> wrote:



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
precursor.



That is all subsumed by the fist point, that this is normal metabolism
for the precursor bacteria.



Why?

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!



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.


bob