Modern mitochondria

[KING2010ORAYL]

can someone please answer and explain this? It would be deeply appriciated!

Modern mitochondria are the descendants of what were once free-living alpha proteobacteria. Insofar as mitochondria become inactive during periods of oxygen debt, what is probably true of thier alpha proteobacterial ancestors?

a. they were obligate aerobes and herterotrophs
b. they were obligate aerobes and autotrophs
c. they were obligate anaerobes and autotrophs
d. they were obligate anaerobes and autotrophs
e. they were facultative anaerobes and autotrophs


i got c. is this correct?

[plasmodesmata11]

Look up rickettsias. Those are the believed closest relatives to mitochondria. That may help.

[JorgeLobo]

"Modern" Mitochondria as a product of endosymbiosis - is a theory, not a fact as you treat it here.

Why would you expect them to have been obligate anaerobes? They possess cytochromes - not usually found in anaerobes - and use oxygen as terminal electron acceptor.

[Sepals]

It's “a” as it was a heterotroph (derives energy from pre-existing food). Autotrophs produce their own food, hence the word “auto”.

[JorgeLobo]

We know the terms. Why would you presume it to be a heterotroph?

[alextemplet]

I don't think the ancestor of mitochondria would've been photosynthetic. It probably started living inside larger cells to have a continuous supply of glucose as well as protection from predators. Heterotroph would be my answer, too.

[JorgeLobo]

Agree - but not all autotrophs are/were photosynthetic

[alextemplet]

True, there's chemosynthesitic organisms, for example. I still think ancestral mitochondria would've been heterotrophs, because living inside another cell would guarantee such a constantly abundant food source. As long as the host cell remains alive, the intracellular parasite has a constant supply of food, so I don't think they would've been autotrophic because there'd be no need for such capability.

As an aside, I think the entire theory of endosymbiosis is one of the most interesting concepts in biology. Although we can't know for sure what the original relationship between the mitochondrial ancestor and its host was, it may in fact have been parasitic. Imagine that! A parasite (which usually means harmful) that acquires such a useful function to its host that the two coevolve to the point that the host cannot live without what once was parasitic!

[JorgeLobo]

Good points. If we accept the concept, you wonder at the relationships that haven't established such a condition such as lichens.

[Sepals]

True, there's chemosynthesitic organisms, for example. I still think ancestral mitochondria would've been heterotrophs, because living inside another cell would guarantee such a constantly abundant food source. As long as the host cell remains alive, the intracellular parasite has a constant supply of food, so I don't think they would've been autotrophic because there'd be no need for such capability.

As an aside, I think the entire theory of endosymbiosis is one of the most interesting concepts in biology. Although we can't know for sure what the original relationship between the mitochondrial ancestor and its host was, it may in fact have been parasitic. Imagine that! A parasite (which usually means harmful) that acquires such a useful function to its host that the two coevolve to the point that the host cannot live without what once was parasitic!

The chloroplast is photosynthetic and it originated the way same. The closest relative to mitochondria are "purple bacteria", which are heterothropic themselves and have the same respiratory system.

The double membrane around the mitochondria signifies originally there was some kind of immune response to it, as intercellular pathogens, such as samonella, also induce this kind of response, where the cell coats these in a lysosome filled with protolytic enzymes to destroy it. Somehow this did not follow through and there was a power struggle, as most of the mitochondrial genes now reside in the main genome in the nucleus. Endosymbiosis is actually more common in nature than you think, it's happened with cyanobacteria (chloroplasts), algea which contain chloroplasts and other organisms which provide some kind of benefit.

These articles explain it in more detail:

http://www.sciencedirect.com/science?_o ... 34a8add72b

http://www.nature.com/nature/journal/v3 ... 109a0.html

[alextemplet]

I wonder what kind of metabolism the ancestors of eukaryotes would've had before they acquired mitochondria. So far the discussion has been solely on the mitochondria themselves; what about the cells they inhabited?

@Sepals - Thanks for those links; interesting stuff!

[MrMistery]

before they had mitochondria? well they were anaerobes, hence why they needed mitochondria when the oxygen levels sored.