Electron Transport Chain

Most of the energy harvested from organic molecules during glycolysis and the Krebs cycle is stored in NADH and FADH2. These molecules give up their high-energy electrons in the third phase of cellular respiration-- electron transport-- where most of the cell's ATP is produced. The electron transport chain is an array of molecules-- mostly proteins-- built into the inner membrane of the mitochondrion.NADH gives up its high-energy electrons to the first complex in the electron transport chain, and FADH2 does this a little farther along the chain. The electrons move from one member of the chain to the next, giving up their energy as they are pulled from NADH toward highly electronegative oxygen. The energy given up by the flow of electrons is used to pump hydrogen ions from the mitochondrial matrix into the intermembrane space. Oxygen captures the electrons in the very last step in electron transport. The last complex adds a pair of electrons to an oxygen atom and two hydrogen ions, forming water.The electron transport chain has used the energy of moving electrons to pump hydrogen ions into the intermembrane space. This buildup of hydrogen ions stores the potential energy that was originally in the bonds of glucose molecules. The backed-up hydrogen ions give up their energy when they diffuse through a special protein in the membrane called ATP synthase. As hydrogen ions flow down their concentration gradient, ATP synthase captures their energy to make ATP. This mode of ATP production is called oxidative phosphorylation because it is powered by the transfer of electrons to oxygen. This process produces 34 ATP.

Above is an animated representation of the Electron Transport Chain. Note that it takes place in the cristae and is an aerobic process.

Notes about the etc.

1 NADH+H+ has enough energy to make 3 molecules of ATP.
1 FADH2 has enough energy to make 2 molecules of ATP.

ATP is the main product of the ETC.

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