Nothing would live without mitochondria.  These are the power centers ubiquitous in all living cells.  They contain molecular machines in factories whose jobs are to generate and conduct electrical currents.  The currents run turbines that packetize the energy in molecules of ATP, which are then used by most processes in the cell.  New discoveries continue to fascinate scientists with how mitochondria work.  Some scientists use their energy to find ways Darwinian evolution could build the machinery of life.

Background.  The energy source for animals is food; for plants, the sun.  Since animals eat plants, or eat other animals that ate plants, sunlight is the ultimate energy source.  In the chloroplasts of plants, sunlight energy is captured to produce energy-rich molecules, including glucose.  Mitochondria have inner and outer membranes.  The inner membranes are folded into protrusions called cristae that increase their surface area.  With the help of transporter machines, the mitochondrion takes in molecules (glucose, pyruvate, and NADH) from the cytosol into its outer and inner membranes into the interior where, with the aid of oxygen and a large number of enzymes and cofactors, electrons are transferred to oxygen through five complexes of machines.  The first three, called NADH dehydrogenase (Complex I), cytochrome c reductase, and cytochrome c oxidase, provide an “electron transport chain” that is used to pump protons into the space between the mitochondrion’s inner and outer membranes.  The protons return through the inner membrane via the fifth machine, the turbine-like rotary motor ATP synthase (see CMI), which uses the proton motive force generated by the other machines to synthase ATP.  Although cells can generate ATP without oxygen (anaerobic respiration), producing it through the mitochondrial machinery is much more efficient.  On a busy day you produce approximately your body’s weight in ATP.  This entry will look at some of the recent discoveries about the machinery of mitochondria.

  1. Machine spacing:  An abstract on PNAS (8/29/2011, 10.1073/pnas.1107819108) described what new images of mitochondria using single particle cryoelectron tomography revealed.  Dudkina et al. could see how Complexes I, III, and IV are organized in mitochondria from cow hearts.  The spacing affects how the complexes interact.  “Surprisingly,” the Dutch and Swiss scientists said, “the distance between cytochrome c binding sites of complexes IIIand IV is about 10 nm.”  Ten nanometers is quite a bit at this scale.  Fortunately, there is a molecular glue – fat – that keeps them in place: “Modeling indicates a loose interaction between the three complexes and provides evidence that lipids are gluing them at the interfaces.”….

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