To be picky: that's only 99.9...% true, because some have lost them again, like Monocercomonoides and Henneguya zschokkei. And they lost the mitochondria by two different mechanisms!
let's keep it going because "parasites" are fascinating. Dodder plants are usually generalized obligate plant parasites. Dodders have "stolen" at least 108 genes from various plants its parasitized.
Bonus, dodder plants also seem to be able to double as a sort of above-ground mycorrhizal network, allowing plants (even across species) to communicate with each other and send warning signals about pests/stressors/etc
your second example is particularly fascinating. Myxosporeans were basically once more complex animals that had gradually evolved towards simpler and simpler structures until they became unicellular organisms again. Henneguya zschokkei seems to have taken this to the extreme — going where not even bacteria ever go
On that note, man o wars are thought to be an example of a complex multicellular organisms partnering so closely that they lose their individualism. Basically every organ of this thing seems to at once have been a separate animal and can still survive on its own for a while
I suppose a better example of what I meant to talk about are lichen. Which are single species but technically a partnership between types of fungi and an algae.
In siphonophores, each specimen is actually a colony of minute asexually reproducing organisms called zooids that have to work together for survival. They are not "independent" in the sense that they would die without each other, but given the fact that they can reproduce independently, there's definitely some sort of independence there. It's like if all your organs were able to independently reproduce themselves.
What I mean is that in Physalia each individual in the floating city is still a clone of the other members of the colony. All members of the floating city came from an unique larva. This mean also that each Physalia is either male or female but not both.
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?]"
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.
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?
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
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".
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?
: 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)
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.
Pardon me but I have to ask, as someone here might know...
Over this past weekend on Saturday afternoon (ET, NYC + PHL markets)[1] on an NPR station (in the car) I heard what I presume was a rebroadcast of a show on a theory about the creation of the first multi-cell organism. Typically, I pick up the name of the show and who the featured guest was, but this time I missed both. It was fascinating stuff and would like to listen to it in full.
Does this ring a bell with anyone?
[1] I realize each NPR station has its own schedule so this clue might not be helpful.
Thanks. Close. That's the same topic / idea, but the bit I heard for definitely longer than 3 minutes. Might have been a 20 mins segment out of 1 hour show.
Still. Thanks. The whole concept is ridiculously beyond comprehension.
I wonder, if antibiotics kill bacteria, and mitochondria are just ancient atrophied bacteria hiding inside other cells, does that mean antibiotics cold be able to kill mitochondria too.
Antibiotics is a category defined pragmatically by the end effect they achieve, killing biological things selectively. They have nothing in common structurally or chemically.
So I guess I want to say that you're asking the wrong question.
> Antibiotics is a category defined pragmatically by the end effect they achieve, killing biological things selectively. They have nothing in common structurally or chemically.
Nice. Thank you. If iodidimonas can be cultured in lab, I bet the researchers that conducted the study posted by OP can try to corroborate their hypothesis by testing if antibiotics more effective against iodidimonas are correlated to those that harm mitochondria the most, when compared to other bacterial groups.
The origin of eukaryotes is an amazing story. The chances of survival of the original combined organism were 0.0000000001%. All the bacterial RNA and DNA that the bacteria produced during life and death were surely messing up with the archaea inner workings, as bacteria and archaea have different genetic code "dialects". The archea had to evolve a nucleus instantly to keep the bacterial RNA away from it's ribosomes.
The survival of eukaryotes may be so unlikely as to even partially explain Fermi paradox.
> The archea had to evolve a nucleus instantly to keep the bacterial RNA away from it's ribosomes.
I heard another theory that it was actually the archea that engulfed the pre-mitochondria rather than the it accidentally finding itself inside an archea. There's some kinds of archea that occasionally grow some extracellular "appendages" and it's conjectured that it may have had some kind of more typical symbiotic relationship with the two kinds of microbes living in near physical contact. What could have happened is that the archea gradually came to fully engulf the protomitochonria with the appendages evolving into being the full body of modern eukaryotes with the nucleus evolving from the functions that were part of the main archean cell body. Some functions got shuffled between the three compartments as this became more of an obligate relationship.
Nick Lane wrote some amazing popular science books on the history of mitochondria;
- Power, Sex, Suicide for a general overview and history of mitochondria (did you know that Lynn Margulis, main proponent of the endosymbiont theory, was once married to Carl Sagan?!?)
- The Vital Question on restraints on life due to the biochemistry of mitochondria
Every single one of his books is amazing and mind blowing. His latest "Transformers" on the krebb cycle is a must read if you're interested in the origins of life.
The theory that eukaryotic cells are just a bunch of bacterial subsystems that happened to start cooperating is one of the cooler points in the biology iceberg. Up there with chickens descended from the T Rex for me.
> The evolution of life on earth has been driven by a small number of major evolutionary transitions. These transitions have been characterized by individuals that could previously replicate independently, cooperating to form a new, more complex life form. For example, [...]
Actually, Archaeopteryx is not an ancestor to chickens either...
Archaeopteryx is offshoot in the evolutionary path leading to birds. It shares a common ancestor with modern birds but branched off in a direction that did not lead directly to them.
> The chances of survival of the original combined organism were 0.0000000001%.
It was surely an experiment attempted many times, as countless bacteria infected countless protoeukaryotes. Probably doesn't explain Fermi paradox, as it succeeded at least twice here on Earth. One for mitochondria, another for chloroplasts.
Sceptical of this. Where did that number come from? What's the uncertainty? Yes, it's an extremely unlikely event, but unlikely events happen all the time. There's just as good an argument that given the advantages conferred by the union, it's bound to be successful given enough iterations.
I'm unfamiliar with research into the difficulty of the second endosymbiotic event that no humans were present to measure and analyze being reduced by the existence of a first endosymbiotic event that has also not been replicated in a lab yet, resulting in another n=1 data point
It's a system to measure endosymbiosis in an organism that's already undergone endosymbiosis so not directly applicable for the entirety of gp's hypothesis, but there's definitely a ton of research into it. There'll always remain a question of if we engineer a system does that work the same way as the evolutionary path since we have the benefit of being non-random/guided by intelligence. It's like with abiogenesis, if we ever figure out a system that lets us reproducibly create life within the timespan of a couple years so we can replicate it and study it reasonably that system almost certainly isn't the original way it happened, but it'll give us good insights into the concepts hopefully
In order to protect its genome from the mitochondrial genome, the host cell had to evolve the nucleus and possibly also sexual reproduction. Once that's done, it works just as well for the chloroplast.
The nucleus is also considered a potential candidate for endosymbiosis [1] and I'd really love to see some actual evidence for your claims at some point instead of just vague handwaving
I appreciate you for calling out the number. It’s ok to say “vanishingly minuscule”. A number may seem insignificant but what was presented was actually precise.
The idea that mitochondria is somehow external organisms that cells co-opted, and somehow became an integral part of every single organism on Earth is one of the most absurd, science fictional things I've ever seen in my life. And yet people just accept this as almost-fact. It's like believing in magic, there's no real explanation as to how something like this occurred, or even what the basic mechanism is, except for one person's speculation that it happened and the idea has spread virally and now it shows up as a fact in articles like this.
Endosymbiotic theory is supported by a wealth of evidence, including:
1) Mitochondria have their own DNA, which is circular and similar to bacterial DNA. This DNA is distinct from the DNA in the nucleus of the eukaryotic cell.
2) Mitochondria have their own ribosomes, which are smaller and structurally different from cytosolic ribosomes. These ribosomes are responsible for translating mitochondrial DNA into proteins.
3) Mitochondria have their own mechanism for protein import, which is different from the protein import machinery of the eukaryotic cell. This suggests that mitochondria were once independent organisms.
4) Mitochondria share many similarities with alpha-proteobacteria, a group of bacteria. This includes the structure of their inner membranes, the arrangement of their genes, and the way they generate energy.
5) Mitochondria reproduce by binary fission, similar to bacteria. This suggests that mitochondria once replicated independently of the eukaryotic cell.
6) The endosymbiotic theory is also supported by the fact that mitochondria are found in all eukaryotic cells, with only a few rare exceptions. This suggests that mitochondria were acquired by an ancestral eukaryotic cell and have since been passed down to all of its descendants.
7) Mitochondria (and chloroplasts) have double membranes, exactly like they would if they were smaller cells engulfed by the host cell.
8) There are multiple examples of ongoing endosymbiosis where the engulfed cell remains a true symbiont, not yet an organelle. Paramecium bursaria is my favorite - a ciliated protozoan with blue-green algae symbionts.
Bonus: there is evidence for secondary and tertiary endosymbiosis too.
"mitochondria is a powerhouse of our cells" its most banal summary used widely of what you aptly summarized. A legacy code of complex life that we cannot get rid of :D
It's been demonstrated in the laboratory and is supported by mountains of evidence. You really do not know what you're talking about.
If you do not understand something, it is better to respond with curiosity than dismissal. I've found that when something seems absurd to me, if I dig in to try to understand it more, it usually turns out my initial reaction was radically wrong.
To be picky: that's only 99.9...% true, because some have lost them again, like Monocercomonoides and Henneguya zschokkei. And they lost the mitochondria by two different mechanisms!
https://en.wikipedia.org/wiki/Monocercomonoides https://en.wikipedia.org/wiki/Henneguya_zschokkei
EDIT: typo