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Comment by gadders | Hacker News Reader

I've never really understood the story of mitochrondria. It's like "This cell absorbed another type of cell [ok so far] but then every future generation of this cell includes the absorbed cell. [<-- How does that bit work?]"

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People used to think it was really rare -- until someone actually recreated it in the lab[0]. In this paper, the researchers created a strain of bacteria (prokaryote) that would only survive if engulfed by modified strain of yeast (eukaryote) that would depend on engulfing said bacteria.

And shockingly, it worked! The engineered bacteria replaced the natural mitochondria in the yeast. Wild.

But I guess to answer your question more directly, the cells that don't have the mitochondria would more likely die, because they don't have the fitness advantage.

[0] https://pubmed.ncbi.nlm.nih.gov/30373839/

Can you elaborate on the part that seems unintuitive?

Eukaryotic cells have multiple copies of their mitochondria, not one. When the cell divides, the mitochondria (roughly) split between the two daughter cells then carry on

From what you have said, I think my mental model for how life forms at the mammal-size level is wrong.

The piece I was missing is that even for large organisms, new life is created by cells (eggs) already containing mitochondria dividing. New cells aren't created from scratch.

> Can you elaborate on the part that seems unintuitive?

For me, the intuitive part is how mitochondria can be created by the body if it's an external structure that's been found. If I take a coin and put it in my pocket, my children don't have any coins at birth. They have to find one themselves. Why is it different for mitochondria?

Mitochondria are self replicating. When the cell splits some of the mitochondria are present in each new cell.

That’s because creation of new coins is external to your reproduction. Eukaryotic cells are not scavenging in the wild for new mitochondria; they control the replication of mitochondria within them, including how they are passed to offspring through reproduction

An interesting thing about mitochondria too— we receive all of our mitochondria from our mother. So for every human, there is an unbroken line of direct mitochondrial ancestors leading all the way back to the first biologically unique Homo Sapian women

From what I've read, Each cell contains from dozens to a hundred+ mitochondrias. When cell splits then some mitos go to one child and some to another.

Yeah, this was how I was thinking as well.

But to continue the analogy, it's more like you split yourself into two smaller "you"s, and in the process each new "you" gets half a coin in the pocket of each new "you".

To clarify, it would be more like you have a group of 10 coins and each of your offspring get 5, but grow back to having 10 during development

Yes, they carry on growing.

Not parent, but there's something missing that leads to the organism becoming stable between generations. Do the mitochondria independently reproduce and it just happens that you end up with neither too many nor too few of them, generation to generation?

https://en.wikipedia.org/wiki/Human_mitochondrial_genetics#R...

: Mitochondrial replication is controlled by nuclear genes and is specifically suited to make as many mitochondria as that particular cell needs at the time.

: Each human cell contains approximately 100 mitochondria

: The amount of mitochondria per cell also varies by cell type

: Egg cell: Mature metaphase II egg cells can contain 100,000 mitochondria

(so when it comes to passing down mitochondria to descendants, eukaryotes don't fool around)

Eukaryotic cells control the replication of mitochondria through signaling pathways

If you can reliably hop the turnstyle and ride the subway for free, then managing to place a friend in two separate cars to be on either side of a planned decoupling doesn't seem like too much of a stretch.

It would be even more miraculous if the cell managed to relate interlopers to just one side for the event. Although you're kind of getting away from cell fission at that point: that's more like birth.

If you're interested in biology, I highly highly recommend the book "Power, Sex, Suicide: Mitochondria and the Meaning of Life" by Nick Lane. It explains the original endosymbiosis and evolutionary process that went on in both bacteria, all the cool stuff that only eukaryotes can do, and why.

Goodreads: https://www.goodreads.com/book/show/39001.Power_Sex_Suicide

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