Posted 04 March 2006 - 05:12 AM
FOr a start, the mitochondrial predecessor prokaryote (assuming the theory is true) didnt infect 'us' in any respect. That symbiotic relationship was clearly formed long before ..well, i'm not sure when, but I am willing to guess it happened before multicellular organisms existed. It is possibly the key factor which started the differentiation from the prokaryote down towards modern day eukaryote? Even if it isn't, mitochondria, afaik, are present in every form of eukaryote cell, even photosynthetic cells...
Start potentially educational section
OK, back to basic biology here: prokaryotes can be grouped into 4 categories of how they obtain energy:
Photoautotroph: use light to drive CO2 into organic compounds. Includes cyanobacteria, and all photsynthetic eukaryotes fall into this nutritional category.
Chemoautotroph: Use CO2 as carbon source and use inorganic substances as energy source. Energy is obtained by oxidizing NH3, FE2+ etc depending on the species.
Photoheterotrophs: Use light to generate ATP, but must obtain their carbon in an organic form.
Chemoheterotrophs: Must consume organic molecules for both energy and carbon
I just put that there so we have some basics to work with, that is where we can get enrgy from theoretically. Actual energy production comes in 3 major forms though: Metabolism, Photsynthesis, and respiration. Our metabolic pathway is Glycolysis, which produces ATP from the breakdown of organic molecules. It does not require oxygen to do this, but there needs to be a way to dispose of the end products. This is done by either fermentation or respiration. Fermentation, i think, makes a little more energy, but still results in organic waste products which need ot be flushed basically (like ethanol and lactic acid). Respiration on the other hand produces CR#P LOADS of energy, and results in water. It is quite possibly the only reason gargantuan behemoths such as ourselves could have possibly evolved: the fact that we can produce enough energy to maintain ourselves from the same amount of fuel.
The theory behind respiration basically revolves around cyanobacteria, the prokaryotes which use CO2, water and sunlight to make O2. When they came to be, they flooded the earth with all of this incredibly harmful molecule, which caused a major selective pressure to adapt or die. Many prokaryotes would have been driven into extinction, some managed to survive in anaerobic conditions, while some were fortunate enough to evolve in such a way where they utilized the oxidizing power of O2 to pull electrons from organic molecules down existing transport chains. "Thus, aerobic respiration may have originated as modifications of electron transport chains co-opted from photosynthesis" (I'm taking this from Biology, by campbel, reece, and mitchel)
From there, the theory goes ancestral prokaryotes formed an endomembrane system (endoplamic reticulum nucleus etc), then it formed a symbiotic relationship with an aerobic heterotroph prokaryote which evolved into the mitochondrion, which is what we have today, while some of them also bonded with a photosynthetic prokaryote, which gave rise to the plant lineage...
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SO, in response to your Question mitohunter/hypermere, obviously organisms exist without mitochondria, but no eukaryotes or higher do. In order to try to remove the mitochondria from a eukaryote, would be a...gargantuan task. But if you did, I doubt the energy produced by glycolysis/fermentation AND photosynthesis would even be enough to maintain a complicated life form. But I have nothing to back that up with. Maybe a combination of organic, inorganic, and phototrophic energy sources would meet the enrgy demands.
But its all very very sci fi and way beyond anything any could possibly do with biology atm. We have trouble changing 1 gene, let alone restructing an entire eukaryotic cellular structure and the supporting genetic code.
