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Mitochondrial DNA

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Mitochondrial DNA

Postby Ciwan » Fri Sep 21, 2007 10:18 pm

Hi everyone

Its my first time here, so go easy on me :D

I wanted to know if there was a difference between the Mitochondrial DNA in humans and the Mitochondrial DNA in other mammals !!

I mean all life on earth has evolved from a single pioneering organism right ? and that organism like everything else that is alive today, must have used ATP as the energy form. So wouldn't it be logical to say that the mtDNA in human cells would be the same as that of Bears, lions, apes ...etc

Please someone tell me the answer, I'm very interested in this.

Thanks
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Postby mith » Fri Sep 21, 2007 10:32 pm

Well, the single pioneering organism probably didn't have mitochondria since the first organism is prokaryotic. So you have some options on how different life forms are related
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You're right, sorry :-)

Postby Ciwan » Fri Sep 21, 2007 10:35 pm

Yes you're right Mith the first organisms were Prokaryotes, sorry my mistake

But you know what I mean, let's say the first Eukaryotic cells :)

All other Eukaryotes must have evolved from that single organism with Mitochondria right?

Help please :)
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Postby mith » Sat Sep 22, 2007 1:27 am

Not necessarily, there might be multiple independent incidents of mitochondrial evolution.
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Interesting

Postby Ciwan » Sat Sep 22, 2007 9:10 am

"Not necessarily, there might be multiple independent incidents of mitochondrial evolution"

very interesting

BUT you said there might be, that would also imply that maybe there was only one incident of Mitochondrial evolution.

So is there no way of knowing for sure (from some source on net or biological papers), if the mtDNA in humans is exactly the same of that of other mammals ?? :( :(
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Postby MrMistery » Sat Sep 22, 2007 11:58 am

yes, there is a way
And it is not!
Why? Well....
Although much more slowly, mitochondrial DNA does mutate. Our mitochondria are constantaly evolving, just like the genes in our nucleus are. Natural selection and genetic drift go for mitDNA just as they do for nuclear DNA. So it makes sense that the more distantly related two species are, the more different their mitDNA will be.

Now, gene migration. Comparing the size of the mitochondrial genomes of various organisms and what genes they do have that slowly and steadily, genes have migrated from mitochondria to the nucleus(see this picture: http://www.ncbi.nlm.nih.gov/books/bv.fc ... iggrp.2613 )

Ok, finally. Independent endosymbiosis. Answer: none as of now. It is still a debate whether all mit arose from the same endosymbiosis or from independent symbiotic events. From what i know, the current opinion in that there were at least three(i have encountered 4 in some books) symbiotic events. But i don't think this is a known fact, it's more of "our best guess". However, even though the number will probably change over the years, it is beginning to look that there were more than one for sure.
Cheers ;)
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awsome

Postby Ciwan » Sat Sep 22, 2007 6:18 pm

Wow Thanks Mistery

That made it all clear, thanks a lot mate :D
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Postby genemachine » Sat Sep 22, 2007 9:39 pm

MrMistery wrote:yes, there is a way
Ok, finally. Independent endosymbiosis. Answer: none as of now. It is still a debate whether all mit arose from the same endosymbiosis or from independent symbiotic events. From what i know, the current opinion in that there were at least three(i have encountered 4 in some books) symbiotic events. But i don't think this is a known fact, it's more of "our best guess". However, even though the number will probably change over the years, it is beginning to look that there were more than one for sure.
Cheers ;)


This is very interesting what you write. In the 5th edition of Stryer's Biochemistry (from 2002) they say that:

"Sequence data suggest that all extant mitochondria are derived from an ancestor of R. prowazekii as the result of a single endosymbiotic event. The evidence that modern mitochondria result from a single event comes from examination of the most bacteria-like mitochondrial genome, that of the protozoan Reclinomonas americana. Its genome contains 97 genes, of which 62 specify proteins that include all of the protein-coding genes found in all of the sequenced mitochondrial genomes (Figure 18.5). Yet, this genome encodes less than 2% of the protein-coding genes in the bacterium E. coli. It seems unlikely that mitochondrial genomes resulting from several endosymbiotic events could have been independently reduced to the same set of genes found in R. americana."

But maybe our knowledge of this has changed since then. Could you point me to the sources where I can read up on this. Thanks!:)

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Postby MrMistery » Mon Sep 24, 2007 10:14 am

I stand corrected. It is the chloroplast endosymbiosis event which is actually believed to be 3 or 4 different events. I got them mixed up. My apologies

However, things are not that clear with mitochondria either.
"What type of bacterium gave rise to the mitochondrion? From sequence comparisons, it seems that mitochondria are descendants of a particular type of purple photosynthetic bacterium that had previously lost its ability to perform photosynthesis and was left with only a respiratory chain. It is not certain that all mitochondria have originated from the same endosymbiotic event, however" MBOC, Alberts et all, 4th edition.
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Postby genovese » Fri Sep 28, 2007 9:12 am

Since mitochondria can be isolated:

Has anybody tried tissue transplanting with mitochondria in human mitochondrial diseases?

Would mitochondria from human tissue be rejected if injected into another human, are they all antigenically tolerated by humans? What about mitochondria from animals - would they be antigencally tolerated by humans.

Would they find their own way into human cells from the blood stream or would they die out before attaining their target?
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Postby MrMistery » Fri Sep 28, 2007 12:55 pm

can a mitochondrium die? there's a question for you. Now, i don't think anyone has tried to transplant mitochondria for the sole purpose that it is hard to isolate them without damaging them and then insert them into a cell. They would NOT find their way into cells. They would be engulfed WBC and digested intracellularly probably
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Postby genovese » Fri Sep 28, 2007 1:48 pm

Thanks for that. Ok lets try some more questions:

If they are to be ingested and destroyed by WBCs surely that must mean that they have foreign antigens on their surfaces?
If this is true, then how can they exist intracellularly?

If one can isolate mitochondria in the lab from fresh tissues, can one keep them alive by giving them the nutrients and missing proteins that are normally provided by their host cells?

If one can do that, should they then be classified as a species in their own right?

Sorry to bombard you with my imagination.
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