Essay:Misconceptions about mitochondria
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A common misconception revolves around the way that mitochondria work. Most people think that "carbs" and oxygen are "burnt" to make water and carbon dioxide as if the mitochondria were miniature furnaces. What really happens is more complicated. First, outside the mitochondrion, glucose is broken down by a series of enzymes to produce a small amount of energy in the form of ATP and a substance called pyruvate. The pyruvate is then sent through a process called the Krebs cycle, which transforms it into CO2 and hydrogen, the latter of which gets carried away by molecules called NADH and FADH2. The hydrogen atoms are broken into protons and electrons, and the electrons are pushed around the membrane between proteins embedded in the mitochondrial membrane and are used to "pump" protons onto one side of the membrane. This creates an imbalance, and through diffusion, the protons attempt to even out their numbers on either side. The flow of protons due to this imbalance is harnessed by an enzyme called ATP synthase, which allows for a phosphate group to join with a molecule called ADP to make ATP. The oxygen one breathes in goes to "mopping up" any excess protons produced by this reaction: otherwise, the chain will back up, so no new ATP can be produced. A cell has only a few minutes of ATP lying around, and when that's gone, glycolysis can't support the cell.