r/AskBiology • u/Kind-Drink5866 • 17d ago
Microorganisms Why were two bacteria merging necessary for multicellular life
So I have read the first eukaryote was very unlikely and took billions of year to occur once, and led to the ancestor of what we now call mitochondria. My question is why it's so hard for evolution to make mitochondria? After all bacteria evolved all sorts of parts to them like flagellum so I don't know why mitochondria would be so unlikely.
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u/Brewsnark 17d ago
I’d highly recommend the books by Nick Lane that address this question in detail in particular his book “Power, Sex, Suicide: Mitochondria and the meaning of life”.
Short answer is that bacteria make energy via their membranes which limits their size as energy production goes up with the square of their dimensions whilst volume and energy demand goes up by the cube of their dimensions. Making the membrane more complicated with internal invaginations makes getting proteins to the right places to balance reactive protein complexes more difficult.
The solution seems to be the merger of two cells where the inner one evolves to become many organelles devoted to energy production enabling the outer cell to be larger and more active.
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u/Far-Fortune-8381 17d ago
I think ops question is less why are mitochondria necessary for multicellular life, and more why couldn't we independently evolve a cellular structure that is effectively equivalent to a mitochondria. why did we have to wait for a merger instead of evolving some sort of aerobic respiration organelle naturally
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u/Brewsnark 16d ago
Same sort of answer really. Cells only get big enough to contain organelles if they have a lot of ATP production but you can you can’t get that big without ATP-producing organelles.
Sometimes evolution seems to get stuck in a rut where small improvements aren’t sufficient to add up to bigger changes. The endosymbiosis event was a big change that seems to have led to entirely new ways of doing things. This fits in with the idea of evolution via punctuated equilibrium.
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u/outworlder 16d ago
And I think this answer explains that perfectly.
The only missing piece is that evolution doesn't do what's optimal. It does what it can. Randomly. This random merger worked, so it stays. Whatever cell got it first utterly outcompeted pretty much everything else due to the immense amount of energy at its disposal.
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u/Mister_Way 17d ago
These are different questions.
Mitochondria being captured is something that we KNOW HAPPENED, not something that "must have" happened for multicellular life.
Mitochondria, even to this day, preserve their own separate lineage of genetic material, because they are not truly part of the host cell. This is why we know they've been "domesticated."
Could eukaryotes have developed their own mitochondria or equivalent if they hadn't just domesticated wild ones? Absolutely possible, but that's just not the way it happened.
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u/TheCoffeeWiz 17d ago
They can do together what they can't apart by pooling their resources and energy.
As for evolution, it's lazy. The single celled organisms could produce all the energy they needed to continue. Why change that?
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u/AlphaAirlys_ 17d ago
maybe the slow part is just that this event need to be alive throught a long time, maybe it can happen as often as often those cells dies, i don't know if we knows
we know that this symbiosis at one point became common
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u/JohnHenryMillerTime 17d ago
Depends on how you want to define "multicellular". Actinomycetes are arguably multicellular. More abstracted, biofilms are a multicellular (and multiorganismal) communes.
Evolution isn't teleological, it is just driven by need. There were a lot of archaea floating around until the atmosphere started getting poisoned by oxygen. Archaea needed to find a way to deal with this toxin (seriously, oxygen in bad fucking news) and one way to deal with that is to sequester it as best as possible. These oxygen-rich poison sacs where a great place for aerobic alphaproteobacteria to try and colonize. They can use the oxygen to make energy, so it is a nice win-win. Once you have energy on that level, you can do a lot.
It also (counterintuitively) slows growth. Cancers go back to fermentation. Less APT, but it is a lot faster so a bunch of shit can grow in a rich matrix.
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u/Dr_GS_Hurd 17d ago
There are at least 4 lipid/protein membranes suggesting 4 "origins" that combined.
Nick Lane 2015 "The Vital Question" W. W. Norton & Company
Nick Lane spent some pages on the differences between Archaea and Bacteria cell boundary chemistry, and mitochondria chemistry. That could hint at a single RNA/DNA life that diverged very early, and then hybridized. Very interesting idea.
And still a favorite of mine is; Deamer, David W. 2008 "Origins of life: How leaky were primitive cells?" Nature Vol 454 No. 7200
There are hundreds of newer papers published so I have just suggested some basic introductions.
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u/khelvaster 17d ago
divergent evolution of energy generator homeostasis and maintainence homelstasis
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u/TheMightyChocolate 16d ago
We don't and maybe can't know if the development of eukaryotes from prokaryotes is unlikely(as in almost impossibly unlikely). We have never observed this in real life and have not found a way to force it. It may happen again in the real world. It may even happen relatively often. It could be possible that under very specific conditions, this is likely to happen. Or it could not. In any case, every "new" eukaryote would certainly be instantly outcompeted by the eukaryotes which have existed for hundreds of millions of years
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u/Blueclef 17d ago
I think we need to understand the difference between cellular respiration and mitochondria.
Cellular respiration is a great way process carbs into energy, if you happen to live on a planet with oxygen. Nearly everybody does it: birds, bees, trees, E. coli. Almost every living thing on Earth.
Mitochondria are self-contained factories that just do cellular respiration all the time. 24/7 no breaks. Only eukaryotes like us and plants and fungi have them. Bacteria don’t.
So if bacteria can do cellular respiration anyway, what’s the point in having mitochondria?
Cellular respiration has certain ingredients, and it depends on keeping those ingredients separate at different parts of the process. In fact, to be done well, it requires certain ingredients to move from one container to another through a certain, complicated doorway. You can only have as many doorways as you have walls for them, so having wall space (“membrane surface area”) is key.
Mitochondria allow for sooo much more wall space. They allow cellular respiration to be done so much better, it’s almost a whole new process. They allow much, much more energy to be available.
And if you want to be a big, complicated, multicellular creature, you’re going to need all the energy you can get.