Other mitochondrion antics have also been noted.

November 2, 2023 6:20 AM

"More than 1.5 billion years ago, a momentous thing happened: Two small, primitive cells became one. Perhaps more than any event — barring the origin of life itself — this merger radically changed the course of evolution on our planet. One cell ended up inside the other and evolved into a structure that schoolkids learn to refer to as the 'powerhouse of the cell': the mitochondrion. This new structure provided a tremendous energetic advantage to its host — a precondition for the later evolution of complex, multicellular life. But that’s only part of the story." Where the heck did all those structures inside complex cells come from? by Viviane Callier, in Knowable Magazine.
posted by mittens (30 comments total)

(I stumbled on this one fortuitously, since I was reading a book mentioned by BobTheScientist and had hit a chapter about how cells evolved to do All The Things, and then read this piece and was absorbed. We are so complicated!)
posted by mittens at 6:23 AM on November 2, 2023 [3 favorites]

That's a fascinating read, thank you.
posted by digibri at 6:59 AM on November 2, 2023

This is deeply cool. One thing I don't really understand is how these theories interact with cell death or division. When they're talking about 'selection pressure' in the context of this crime-fighting team of archaea and mitochondrion, which haven't yet merged into a single entity, how does that 'pass on' its arrangement to future generations?
posted by doubleozaphod at 7:08 AM on November 2, 2023 [1 favorite]

Thank you for this!

One thing I recently realized is that all these things take place more or less in total darkness. Not in the bright pinks, purples, and yellows of our textbooks or the backlight of a microscope. These entities are sightless.

"Endoplasmic reticulum" is another one of those phrases that lodged into my head. It probably came from this book I had as a kid, The Magic Anatomy Book, where two children fell into the titular book and had to have a bunch of adventures on the cellular level before getting out.
posted by Countess Elena at 7:10 AM on November 2, 2023 [2 favorites]

Every time I look at cellular biology I'm just stunned that any of this works at all. The mechanisms of cellular life are ridiculously complex. The only way I can wrap my head around this system evolving at all is to remember that the current estimate of the number of cells on earth is on the order of 10³¹. That's a lot of tiny test tubes.
posted by phooky at 7:19 AM on November 2, 2023 [4 favorites]

how does that 'pass on' its arrangement to future generations?

If you're in the mood for a bad analogy, imagine you're on a wooden pirate ship, and there are rats aboard.
You decide to build a new ship while still at sea (otherwise you'd break the analogy), and you do so from timbers and crew pillaged from other vessels. When it's ready, half of the available crew and half of the remaining supplies get transferred to the new ship.

Will your new ship also have rats?
posted by Acari at 7:20 AM on November 2, 2023 [3 favorites]

This new structure provided a tremendous energetic advantage to its host

The first cavalier...
posted by trig at 7:21 AM on November 2, 2023 [4 favorites]

Every schoolkid gets that 'powerhouse of the cell' level learning in their early years, but my true understanding of the mitochondria came from that classic source of higher education, Parasite Eve.
posted by FatherDagon at 7:37 AM on November 2, 2023 [3 favorites]

Pretty sure Battlestar Galactica wrapped up this mystery for us.
posted by Zargon X at 7:47 AM on November 2, 2023 [2 favorites]

I really appreciate science writing at this level. It's not dumbed down, it's communicating a lot of complex ideas. But it's accessible, written clearly for a generalist audience. It's a rare genre these days.

Does anyone read Knowable Magazine regularly? Is it usually this good? It looks appealing on the website. Some of the headlines seem a little clickbaity but the articles have substance. They have a good RSS feed.

It's published by Annual Reviews, a non-profit that has a bunch of publications, mostly, well, annual reviews of synthesis from various academic disciplines.
posted by Nelson at 7:47 AM on November 2, 2023 [5 favorites]

I learned from A Wind In The Door that mitochondria are the elementary school principals of the cell.
posted by phooky at 7:48 AM on November 2, 2023 [7 favorites]

What better way is there to learn to understand protein synthesis than with interpretive dance?
posted by Multicellular Exothermic at 8:11 AM on November 2, 2023

This was a fun and informative read!

However you missed the highlight - one of the researchers (at University College in London) is named Buzz Baum.
posted by skyscraper at 9:04 AM on November 2, 2023 [2 favorites]

I love the endosymbiotic theory! It's amazing and beautiful and confusing, just like all good biology.

However, I think Lynn Margulis deserves more than the brief two sentences she gets here. She didn't simply "articulate[] her theory of endosymbiosis." She fought tenaciously for years against absolutely batshit levels of misogyny and sexism to get her work out. She was told by grant reviewers, "Your research is crap. Don't ever bother to apply again." Her ground-breaking 1967 work that is now celebrated was rejected fifteen times before she could find just one editor who was open minded enough to see the value, and at least willing to entertain the thought that a woman could do amazing work that challenged the current understanding.

We've come a long way in our understanding of the origins of complex organelles since 1967, but we'd be a fuck of a lot further if not for the shitty patriarchical system that held her down. And we'd be a lot further behind if she hadn't been not only such a great scientist but also possessed such perseverance in the face of open derision and hostility. We've also come a long way in treating women less horribly in science, but we still have a long way to go!
posted by SaltySalticid at 9:15 AM on November 2, 2023 [26 favorites]

I learned from A Wind In The Door that mitochondria are the elementary school principals of the cell.

Part of me to this day still insists that farondolae are a real thing.
posted by grumpybear69 at 10:06 AM on November 2, 2023 [1 favorite]

(Speaking of, I think I've recommended this book here before, but David Quammen's The Tangled Tree tells a lot of the story of Margulis's work and its reception--both its rejection and its later absolute necessity for our thinking--in a very readable way.)
posted by mittens at 10:07 AM on November 2, 2023 [2 favorites]

@nelson

I subscribe to their weekly newsletter and donate to them annually. It really is this good. It is one of the better magazines for science. Quanta and Aeon along with the weekly NYT Science Weekly are my other subscriptions.
posted by indianbadger1 at 10:11 AM on November 2, 2023 [2 favorites]

These entities are sightless

Not only sightless, but mitochondria are only just barely large enough to reflect visible light. Most viruses are even smaller and cannot be seen with visible light. They have no color, as we understand it.
posted by They sucked his brains out! at 10:14 AM on November 2, 2023 [1 favorite]

I'm kind of surprised that none of these theories really discuss the host cell. The mitochondria fulfills a specific role - ATP generation, and presumably that was something the host wasn't good at.*

There are cells that don't do any energy generation. Viruses. Mimivirus has a genome that's large relative to most viruses (1.2 Mbp), if small relative to eukaryotes. As a virus it has all the machinery necessary to replicate, but also tRNAs and components of primary metabolism. If it got an intracellular parasite it would be pretty close to a proto-eukaryote.

*Eukaryotes are much more acid-tolerant than many prokaryotes, just because the mitochondria is sequestered in the cytosol and is so separated from the external pH. Fungi use this to great effect, releasing a ton of organic acids into soil to prevent bacteria for competing with them.
posted by Orange Pamplemousse at 10:32 AM on November 2, 2023 [4 favorites]

*Eukaryotes are much more acid-tolerant than many prokaryotes, just because the mitochondria is sequestered in the cytosol and is so separated from the external pH.

Is this somehow connected to the mechanism that mitochondria use to phosphorylate ADP? If I remember correctly, the mitochondrion uses the energy from every step of breaking sugars apart not to directly make ATP, but to stuff its own interior full of H+ ions. So I would expect its interior to be really acidic. (It then lets the H+ come out of the interior- IF that H+ pays the energetic toll of turning ADP into ATP).
posted by a faded photo of their beloved at 11:19 AM on November 2, 2023 [1 favorite]

I'm always a bit confused why it's framed as "this archaea engulfed a bacterium, and now we have mitochondria" when in my head it makes more sense to think "this bacterium parasitized an archaea, and now it's an endosymbiont that cannot survive without it's original host"

If an archaea engulfs something, it's because it is eating it.
posted by caution live frogs at 12:20 PM on November 2, 2023 [2 favorites]

Symbioses can be commensalistic, mutualistic, or parasitic, and knowing the full scope of which effects are positive and negative to which players can be surprisingly difficult, even if they are right there in front of you! You can also think of them just living really close, maybe attached, and both benefiting, and as they cozy up, one sort if fits inside the other, like the rhizobia engulfed by root nodules.
Even actual eating doesn't always mean digestion. Those sea slugs that manage to eat chloroplasts and then incorporate them into themselves.
posted by SaltySalticid at 12:52 PM on November 2, 2023 [1 favorite]

Are we sure that some mitochondria didn’t get a good deal on a fixer-upper opportunity and just started doing home repairs, but got carried away and accidentally built a metropolis?
posted by GenjiandProust at 1:24 PM on November 2, 2023 [1 favorite]

In grad school 40 years ago, I sat at the feet of Lynn Margulis through her BI504 Evolution course. The Phanerozoic (everything since the Cambrian = almost everything you&me recognise as life incl all plants, animals and fungi) was relegated to the last week of the semester as an interesting appendix to the main story which was all about the Embden-Meyerhoff pathway, stromatolytes . . . and endosymbiosis. Contra the Article, Margulis was sure that peroxisomes [and flagella, cilia] were the result of independent endosymbiotic events.

Which is a big ask on the evidence front because, while mitochondria have a teeny-tiny reduced genome that can be compared to the rest of life [and bingo α-proteobacteria turned out to be the closest match], peroxisomes have lost all their DNA and have to import all the proteins=enzymes necessary to carry out their business. The article gives an alternative view to this hypothesis . . . with evidence. Interestingly many species of α-proteobacteria are even today endosymbionts or intra-cell pathogens - Wolbachia, Rhizobium, Rickettsia to name three.

If you fancy a long bet against Margulis being correct that peroxisomes were an independent acquisition rather than a handmaiden of mitochondria, I wave my $1 bill at you.
posted by BobTheScientist at 1:54 PM on November 2, 2023 [10 favorites]

a faded photo of their beloved, it's because the gradient that the mitochondria uses to make energy is ultimately one between the inside of the mitochondria and the inside of the cell (matrix vs intermembrane space, but close enough. The energy from breaking down sugars is used to pump protons out of the mitochondria, into the cytosol. The inside of the mitochondria is basic.

The gradient that bacteria have to use is between the inside of the cell and the outside of the cell. If fungi make the outside acidic it because much harder to pump protons out of the cell and make energy when they flow back in. The obvious answer would be to acidify the cell, reducing the difference in pH, but that would interfere with a lot of different cellular processes.
posted by Orange Pamplemousse at 7:36 PM on November 2, 2023 [2 favorites]

Lynn Margulis is one of my heroes, though I never met her. The story of how she persevered in genius despite all the rejection is inspiring. One might want to believe that such things happened in the bad old days, but certainly not now... however, this year's Nobel prize winner Katalin Kariko has a similar story. Sometimes I think great breakthroughs in science are not limited by people's intellect or technical skills, but rather by their emotional ability to remain productive despite being miserable.

That said, thought-provoking articles like this certainly help make my day less miserable. Fascinating.
posted by brambleboy at 7:53 PM on November 2, 2023 [2 favorites]

One thing I recently realized is that all these things take place more or less in total darkness.

Another thing that textbook diagrams fail to convey is just how frenetic everything is on a molecular scale. Everything is vibrating and jiggling with Brownian motion. These are warm aqueous systems with soft structures. Anything not anchored down is bouncing around against everything else. Cellular machinery doesn't just tolerate this, it depends on it. You need a certain amount of random motion so that Part A can find Part B. Diffusion is how a lot of soluble material gets moved around. And things can move fast. Some enzymes operate at a frankly incomprehensible speed. Carbonic anhydrase, for instance, performs something like 10⁶ reactions per second. It's what’s known as a diffusion-limited enzyme, which is a boring way of saying that it operates faster than substrate can get to it. It has evolved to the uppermost limit of what is functionally possible.
posted by dephlogisticated at 8:43 PM on November 2, 2023 [5 favorites]

Archaea are extremely difficult to grow in a lab, so that they can be studied, but progress is being made and the archaea most closely related to us (but lacking internal mitochondria) are complex enough to suggest a later endosymbiosis with mitochondria late. Or at least somewhere between early and late. They also seem to depend on a close relationship with sulfate-reducing bacteria, so they may have developed mutualism with the ancestors of mitochondria long before the endosymbiosis event.
posted by johnabbe at 5:28 AM on November 3, 2023 [3 favorites]

The energy from breaking down sugars is used to pump protons out of the mitochondria, into the cytosol. The inside of the mitochondria is basic.

The gradient that bacteria have to use is between the inside of the cell and the outside of the cell. If fungi make the outside acidic it because much harder to pump protons out of the cell and make energy when they flow back in.

Excellent! Thanks for tying those pieces together Orange Pamplemousse!
posted by a faded photo of their beloved at 9:03 AM on November 3, 2023

Huh, Lynn Margulis used to be married to Carl Sagan too!
posted by omegajuice at 2:05 PM on November 9, 2023