Explanation of Electron Transport Chain (ETC)

Electron Transport Chain      When the reduced coenzymes produced by the Krebs cycle (NADH, FADH2 ) are oxidized energy is released. The electron transport chain (residing in the inner membrane of the mitochondrion) is designed to convert that energy into a form that can be used to produce ATP. The electron transport consists of a set of protein complexes in the inner mitochondrial membrane. Most are proteins and all are designed to capture and release electrons at various energy levels. Some of the proteins are cytochromes that contain hemes, iron containing chemical groups that are also found in hemoglobin. Other proteins are iron-sulfur proteins which contain iron atoms bound to sulfur. Coenzyme Q is not a protein but a small molecule that is essentially a hydrocarbon.       NADH releases its electrons to the electron transport chain. The electrons are accepted by flavin mononucleotide  (FMN) which releases it to an iron-sulfur protein which passes it on to Coenzyme Q (mobile carrier). The electron continues along a chain from cytochrome b to another iron-sulfur protein to cytochrome c1 to cytochrome c (mobile carrier) to cytochrome a to cytochrome a3 to an iron-copper protein and finally to O2 . At each step along the chain the electron goes from a higher energy level to a lower one.      As electrons pass along the transporters of this chain, the three complexes in which these transporters are arranged uses the energy that is released to transport a hydrogen ion (H+) from the mitochondrial matrix to the intermembrane space against its concentration gradient. This creates a concentration gradient across the inner mitochondrial membrane with a high concentration of H+ in the intermembrane space compared to the mitochondrial matrix.      The H+ moves down its concentration gradient through an enzyme in the inner mitochondrial membrane called ATP synthase. The energy released as H+ flows down its concentration gradient is used by ATP synthase to phosphorylate ADP to ATP. This process is called chemiosmotic coupling.      The overall reaction for oxidative phosphorylation is:      When all the stages of glucose oxidation are taken together the net results is: glucose + 6O2 + 38ADP + 38Pi ® 6CO2 + 6H2O + 38ATP