So, a thought came up and I couldn't find all that much info online, so I thought I'd ask some professionals here!

The endosymbiont theory states that: mitochondria came to be ingested by bigger prokaryotic cells about 1.8 bYa, and by chance of luck came to a mutualistic relationship.

Now, mitochondria are said to have been archaea, right? But the mitochondria in our cells have phospholipid bilayers, with ester bonds in them, like all eukaryotes, but when you look at archaea, you see that they have monolayers because of their ether bonds, with rings and all sorts of branching, which is what gives them that extremophile-acclaimed resistance.

Question is if the endosymbiont theory is so widely accepted and mitochondria are meant to be archeae, why do they not present a monolayer with ether bonds?

Thanks for your time!

  • 1
    $\begingroup$ Only some archaea have a monolayer others have a bilayer, and the monolayer is believed to be a derived adaptation for extreme environments. $\endgroup$
    – John
    Commented Feb 9, 2018 at 14:46
  • $\begingroup$ @xusr — I was going to make the same point, suggesting the poster change his question to why don't eukaryotes have an archae-like cell membrane. But rather as a joke. If you think about it, eukaryotes are assumed to have evolved from prokaryotes but in either case they don't have a cell wall. So the enclosing structure of eukaryotes evolved from that of their prokaryotic ancestor at some time. Anyway, that's a separate question. $\endgroup$
    – David
    Commented Feb 9, 2018 at 17:41
  • $\begingroup$ I think there is a typo or a misconstruction in the sentence before the one I take issue with. "The endosymbiont theory states that: mitochondria came to be ingested by bigger prokaryotic cells ". Whatever was ingested was not a mitochondrion, but a prokaryote that became a mitochondrion. You should tidy this up. $\endgroup$
    – David
    Commented Feb 9, 2018 at 17:45

2 Answers 2


I think the question is based on a false premise:

Poster: Now, mitochondria are said to have been archaea, right?

Me: Wrong, I’m afraid.

The closest bacterial relation of mitochondria is Rickettsia, an alpha-Proteobacterium (see Lang et al. for a review). Rickettsia is a eubacterium, not an archaebacterium.

The confusion is probably due to misreading one of the two alternative theories of the origin of mitochondria. This is the theory that the host for the original mitochondrion was an archaebacterium (rather than a primitive nucleated eukaryote). In both theories this host aquired a eubacterium related to Rickettsia, which gave rise to the mitochondrion.

  • $\begingroup$ Ah, great reply! The actual misunderstanding had come from one of my teachers actually (actually just a PhD who got to give us a few lectures), you cleared it up! $\endgroup$ Commented Feb 9, 2018 at 19:45
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    $\begingroup$ @FedericoParravicini — Don't be too hard on your teachers. It's easy to make a mistake, especially if the main focus of your lecture is elsewhere, or even to trip over your tongue (a verbal typo). What I would recommend is to use web resources to check these things. I prefer text books to random websites or Wikipedia, as they are integrated and subject to editorial review and often well illustrated. If you don't have access to a good library try NCBI Bookshelf, which has old editions of some reputable texts such as Berg, Alberts and Lodish et al. $\endgroup$
    – David
    Commented Feb 11, 2018 at 11:49

During the process of phagocytosis, the host membrane surrounds the food. So in this case, these bacteria were surrounded and encased in the host membrane, which pinched off internally, and became the outside membrane of the mitochondria.


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