General ---------Biology----------------------------------------------------- ------------------Online--------------------------------------- Ch. 9 Cellular Respiration: Harvesting Chemical Energy

Oxidation = removal of electrons and phosphorylation = phosphorylation of ADP to form ATP. 

Recall that oxidation is the removal of an electron.  Also recall that electrons are like sticky fly paper; for a molecule to loose an electron, under normal circumstances, an adjacent molecule with a stronger affinity for the electron must pull it away.  When the electron is transferred, some energy is given off as heat and some is used to drive ATP production. 

When NADH dumps its electrons, the electrons are at a very high energy level.  The job is to let the electrons down in a series of small steps, passing them from molecules to molecule in a series of redox reactions:  oxidation-reduction, oxidation-reduction, etc., etc.  By lowering the energy level of the electron in small steps, you avoid a small explosion or intense heat, and the energy is available for making ATP.  Click here to see illustration.

There are nine proteins embedded in the inner mitochondrial membrane;  NADH dumps an electron at the top end of this chain, and then it is passed from one protein to the other, giving off a small amount of energy at each step.  At the end of this electron transport chain,  oxygen accepts the spent electron.  When you inhale, the oxygen that enters your blood stream is headed to the mitochondria and specifically to the end of the electron transport chain.  Oxygen is called the terminal electron acceptor.

If you want to experience the electron transport system in your cells, then hold your breath for 20 to 30 seconds.  The sensation you feel results from the electron transport chain coming to a stop, and you begin to run out of ATP.  If there is no oxygen to accept the electron from the last protein, then the electron stays on the last protein.  This causes electrons to back up through the electron transport chain, stooping oxidative phosphorylation.  It is like the only road out of town is blocked, and traffic backs up causing gridlock through out the Krebs Cycle and Oxidative Phosphorylation.  Only Glycolysis is outside the mitochondria, and without oxygen Glycolysis is the only pathway that can continue to flow.