1. Mitochondria are small, round to oblong organelles only found in eukaryotes. They don’t look like much on the outside, but they have a complex structure consisting of a double membrane system with a large surface area for housing enzymes.
  2. To understand the role of mitochondria, it is helpful to know something about energy transformations in cells. Energy is required to perform the myriad molecular tasks that keep a cell alive and functioning.
  3. Glucose is often thought of as an energy source. This is only true because of the action of mitochondria, which ultimately are responsible for generating the cell’s true energy currency.
  4. This true cellular energy currency is adenosine triphosphate, better known as ATP.
  5. Anywhere a small energy “kick” is required (to assist an enzyme in its action, for example), one of the three phosphate (PO43-) groups on an ATP molecule is removed and added to some receiving substrate molecule.
  6. The donation of the phosphate group changes the ATP to adenosine diphosphate (ADP). The receiving molecule has been phosphorylated.
  7. The phosphate molecule can be removed from the substrate and added to an ADP to convert it back into ATP once again. It is this specific and highly localized on-off exchange of phosphate groups that releases energy to drive chemical reactions within the cell.
  8. ATP is a big deal, and that is where mitochondria come in. In plants, the glucose resulting from photosynthesis is split into two pyruvate molecules. Pyruvate then enters the mitochondria where it is transformed by dozens of orchestrated reactions to generate 30 ATP molecules for every starting glucose molecule.
  9. An important phase of the ATP production process occurring inside mitochondria is the citric acid cycle (a.k.a. the carboxylic acid cycle or Krebs cycle), the elucidation of which led to a Nobel Prize for Hans Krebs and Fritz Lipmann in 1953.
  10. Mitochondria are able to fuse and, like chloroplasts, they contain their own DNA and multiply in a way that looks a lot like bacterial fission. According to endosymbiont theory, both mitochondria and chloroplasts are derived from prokaryotes that were taken up by host cells in the early days of life on Earth.