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Mitochondria and the origin of eukaryotes

knowablemagazine.org

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Re: Mitochondria and the origin of eukaryotes

#21

Post by ajuc »

echelon wrote: post #18
JumpCrisscross wrote: post #14

Earlier quoted context omitted.

> can we estimate how many planets in the galaxy have eukaryotes? Not yet. In the history of life on Earth, this has happened once. Knowing what we know about cellular biology, it’s stupidly unlikely. Beyond our present theories’ ability to quantify. By the way, I think this is one of—if not the—great filters. It’s unlikely to happen, to not promptly get smote by its primordial planet’s tantrums and to get it so righ…

> Not yet. In the history of life on Earth, this has happened once. 1) That we know about. 2) Not unlike startups vs. established business, any newly emerging "eukaryotes" have to out-compete the already-evolved incumbents, which are already quite good at harnessing energy. You're much more likely to find success in business than in an entirely new evolutionary branch, though I doubt biological "gray goo" is outright…

Additionally the environment changed significantly since then (for one example oxygen which was highly toxic to most forms of life that existed back then is now over 20% of atmosphere).

> Reverse chirality autotrophs sound like a scary sci-fi novel plot

Very ice-9-like.

Re: Mitochondria and the origin of eukaryotes

#24

Post by edgyquant »

ncmncm wrote: post #10

If they find cells lacking some organelle, it will be hard to say whether it was never acquired, or was later abandoned. One clue would be leftover genes from when it was there. Eukaryotes often find it hard to prune out excess DNA, vs. just turning it off.

DNA doesn’t help as much as you think with single celled organisms thanks to HGT. Bacteria, at least, share DNA and thus we can’t use it to determine a linear evolutionary sequence.

Re: Mitochondria and the origin of eukaryotes

#25

Post by reubenswartz »

anton96 wrote: post #19
frostburg wrote: post #8

Earlier quoted context omitted.

Presumably like we do - (I'm heavily simplifying the complex regulation involved) the mitochondria have their own DNA which gets duplicated when the cell prepares to undergo mitosis, then the two new cells split the results.

Does that implies that mitochondria also had to evolve at some point to detect duplication of their host cell so they duplicate at the same time?

There are lots of mitochondria in a cell (almost always, ignore red blood cells, for example), and the mitochondria have their own mechanisms for detecting when they need to divide (exercise and the resulting stress being one of them, which is why working out makes you more fit).

Also note that the DNA for most of the mitochondrial proteins is in the host cell's nucleus-- the mitochondrial DNA is stripped down to coding for just a few essential proteins.

Re: Mitochondria and the origin of eukaryotes

#26

Post by ssl232 »

majkinetor wrote: post #5
alangibson wrote: post #2

> For billions of years after the origin of life, the only living things on Earth were tiny, primitive cells resembling today’s bacteria I've often used this "fact" as an argument against complex extraterrestrial life. Glad to see it might be wrong after all.

This is Nick Lane's argument - that complex cell happend only once on Earth (no convergent evolution) via this symbiotic accident and hence it's highly improbable if not almost impossible. As usual, people always seem to foreget that in this universe, what happened once, happens all the time and we are not special.

Nick Lane's book The Vital Question is a masterpiece. I reckon he's figured out the origin of life there. I hope he gets on some podcast like Lex Fridman to talk about it all, because his ideas are just waiting to explode into the public imagination.

Re: Mitochondria and the origin of eukaryotes

#27

Post by ncmncm »

edgyquant wrote: post #24
ncmncm wrote: post #10

If they find cells lacking some organelle, it will be hard to say whether it was never acquired, or was later abandoned. One clue would be leftover genes from when it was there. Eukaryotes often find it hard to prune out excess DNA, vs. just turning it off.

DNA doesn’t help as much as you think with single celled organisms thanks to HGT. Bacteria, at least, share DNA and thus we can’t use it to determine a linear evolutionary sequence.

Eukaryotes don't do so much of that.

Re: Mitochondria and the origin of eukaryotes

#28

Post by marcosdumay »

CRUDite wrote: post #12

If we assume single celled life is common, and exists in either all star systems, or in all systems without a hot Jupiter close to the star; then given the length of time involved here before eukaryotes, can we estimate how many planets in the galaxy have eukaryotes? Or how long it will be before some do? Presumably increasing the length of time increases the probability of occurrence as would increasing the number o…

Well, that's not a good assumption to make. Our most capable life detector¹ is analyzing the atmosphere of planets, captures stuff similar to our simplest single celled life. So, it's not a good guess that it's common.

1 - Actually our second best. The best one is the fact that nobody colonized Earth before we existed, that is tuned in space-faring life.

Re: Mitochondria and the origin of eukaryotes

#29

Post by marcosdumay »

majkinetor wrote: post #5
alangibson wrote: post #2

> For billions of years after the origin of life, the only living things on Earth were tiny, primitive cells resembling today’s bacteria I've often used this "fact" as an argument against complex extraterrestrial life. Glad to see it might be wrong after all.

This is Nick Lane's argument - that complex cell happend only once on Earth (no convergent evolution) via this symbiotic accident and hence it's highly improbable if not almost impossible. As usual, people always seem to foreget that in this universe, what happened once, happens all the time and we are not special.

> that complex cell happend only once on Earth

Well, it's quite possible that once it happens, it voids any chance of it happening again just because life filling that niche already exists. If so, it only happens once, and this says absolutely nothing about the odds of that first occurrence.

> what happened once, happens all the time

That's a fallacy people do all the time here when talking about exobiology. It's basically states that all small numbers and all big numbers are alike, and that all small numbers are like the inverse of all big numbers.

Re: Mitochondria and the origin of eukaryotes

#30

Post by prox »

majkinetor wrote: post #5
alangibson wrote: post #2

> For billions of years after the origin of life, the only living things on Earth were tiny, primitive cells resembling today’s bacteria I've often used this "fact" as an argument against complex extraterrestrial life. Glad to see it might be wrong after all.

This is Nick Lane's argument - that complex cell happend only once on Earth (no convergent evolution) via this symbiotic accident and hence it's highly improbable if not almost impossible. As usual, people always seem to foreget that in this universe, what happened once, happens all the time and we are not special.

And that is if there is only one universe, which might not be so special as well.
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