According to endosymbiotic theory, animal cells acquired mitochondria for better respiration and energy production. Then how did animal cells thrive before they acquired mitochondria?
Dear Hasnahana, I agree with Rob and can add that some cells are actually functioning without mitochondria at all - tumor cells (not all and not totally without, but still...) - try to surf "Warburg's effect" through any database... It's really interesting... There is a rising interest for role of mitochondria in sepsis, inflammatory diseases and so on...
By the way mitochondria did not come to animal cells as they are now. This symbiosis has a long history of mutual benefit exchange starting with two nearly equal cells (size) one of which was engulfed by another (simplified picture) resulting in eukaryotes in existing diversity which would not be possible without mitochondria (true multicellularity is not possible without mitochondria). And this relationship is not done yet, this complex of host cell and endosymbionts (mitochondria/chloroplasts) is still evolving, so let's see what it will be in some 300 million years in future ;)...
Best regards!
Rather polyphosphates were among the first macroergs in living systems. The polyphosphate system works well now in prokaryotes, but are still in eukariotes too.
Dear Hasnahana, I agree with Rob and can add that some cells are actually functioning without mitochondria at all - tumor cells (not all and not totally without, but still...) - try to surf "Warburg's effect" through any database... It's really interesting... There is a rising interest for role of mitochondria in sepsis, inflammatory diseases and so on...
By the way mitochondria did not come to animal cells as they are now. This symbiosis has a long history of mutual benefit exchange starting with two nearly equal cells (size) one of which was engulfed by another (simplified picture) resulting in eukaryotes in existing diversity which would not be possible without mitochondria (true multicellularity is not possible without mitochondria). And this relationship is not done yet, this complex of host cell and endosymbionts (mitochondria/chloroplasts) is still evolving, so let's see what it will be in some 300 million years in future ;)...
Best regards!
As pointed by Dauren, there was no "animals without mitochondria". When the animals (Metazoa) had their origin, the precursor cells that lead to multicellularity were already endosymbiontic, eukaryotics cells.
So the proper question should be: How cells without mitochondria produced ATP so far? And the answer, lies in how prokaryotes live.
Glycolysis is the process by which anaerobic cells including bacteria and yeast ferment sugars to other organic compounds. This does not require mitochondria which carries out the Citric acid cycle /Krebs cycle aerobically (requiring Oxygen) or another electron acceptor in anaerobic respiration. Giardia duodenalis, an anaerobic eukaryote that does not have mitochondria answers this question. See this article http://www.mitochondrial.net/showabstract.php?pmid=9504342.
There is no reason why purine analogs (like plain adenosine) could not be taken up by the proto cell before endosymbiosis occurred, and this internalized purine converted to ATP by a phosphotransferase using phosphate. The 'evolution' of mitochondria made the generation so efficient, that it was a huge conserved evolutionary advantage and was selected for.
Also, there are other 'less efficient' methods of storing and using energy than ATP in cells today. There is no a priori reason that ATP was the "only" energy molecule utilised by the proto cell.
Prem Subramaniam, I didn't give it a thought but yes, there could've been an alternative energy currency for proto cells. Very intriguing!
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