Why do mitochondria have a phospholipid bilayer? 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!

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.