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I wonder whether there is any intelligent decision-making in mitochondria in the timing of their operation.

Do they simply begin ATP production as soon as the correct reactants are present?

Or, because they have their own DNA, do they have more complex strategies that vary to benefit the mutual cooperation with the host cell? This assumes that the simple circular DNA is performing higher level decisions in switching.

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Mitochondria only have a handful of genes; their regulation is utterly intertwined with their host. Additionally, only the TCA (Krebs, Citric Acid...) cycle occurs within mitochondria; glycolysis occurs in the cytosol. –  Nick T Jan 24 '12 at 0:17
@NickT, does that imply that the host 'controls' the activity of mitochondria? –  Vass Jan 24 '12 at 9:56

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Mitochondria are comprised of ~3000 proteins. However, the mitochondrial genome has only 13-14 protein-encoding genes. The remaining 99.6% of mitochondrial proteins are encoded by genes in the nuclear genome. (Wikipedia) Chloroplast genomes are only slightly larger (~100 genes).

Gene regulation and signaling between the nucleus and mitochondria (and between nucleus & chloroplast in plants/algae) occurs in both directions. Anterograde regulation is the signalling from nucleus to mitochondria and was once thought to be the only method of regulating organelle function. We now also know that Retrograde regulation occurs, in which the mitochondria sends signals to the nucleus.

To answer your question directly (but not thoroughly), both the mitochondria and the nucleus are sensing the environment and needs of the cell and signaling to each other to regulate ATP production.

If you want to learn more about retrograde signaling, googling "retrograde regulation" will bring up lots of papers on this topic in different organisms. This paper also has some diagrams of signalling pathways.

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this is very interesting how there is bilateral communication between DNA and mitochondria. Does mitochondria have to work to survive? Eg. if they do not produce ATP, do they die? –  Vass Jan 24 '12 at 10:08
Hi @Amy =) Whilst I know that your block is quite small, we're trying to discourage extended direct quotes from wikipedia (see meta). It might be a better idea to summarise the article yourself and link to it as a source for your answer =) –  Rory M Jan 24 '12 at 18:37
@RoryM - edited :) –  Amy Jan 24 '12 at 18:57
@Vass That's what I think is the coolest thing about eukaryotic cells. The cell cannot build a mitochondria "from scratch" because the mitochondria have kept just enough genes on their own genome - but mitochondria cannot survive outside the cell because it has lost so many genes. If they don't produce ATP, they die, because the cell dies. Both the cell and the mitochondria have a vested interest in keeping the machinery going. :) –  Amy Jan 24 '12 at 19:03
@Amy, why is this symbiosis so much more beneficial than the scenario of all regulation being contained in the nucleus? –  Vass Jan 24 '12 at 19:19

The textbook version for the regulation of ATP involves a feedback loop with phosphofructokinase (PFK). The relative concentrations of ADP and ATP are characteristic of the energy state of the cell. If the cell is using energy, then there will be an excess of ADP. If not, then ATP.

ATP is an inhibitor of PFK, which in turn slows glycolysis (thus reducing the production of new ATP). In contrast, ADP is an allosteric activator of PFK, which in turn speeds up glycolysis (thus increasing the production of ATP).

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so there is a stable equilibrium concentration between these two compounds? And is it that the use (or lack of use) of ATP ignites the production of more ATP from ADP? –  Vass Jan 24 '12 at 10:00

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