Electron Transport


Electron Transport Essay, Research Paper

Electron Transport Essay

Electron transport is the last phase and most important phase of cell respiration. It accounts for most of the ATP made in cell respiration. Cell respiration makes a total of thirty eight ATP?s, two from Glycolysis, two from the Krebs cycle and thirty four from electron transports. Electron transport takes place after Glycolysis and the Krebs cycle. Glycolysis and the Krebs cycle make their ATP through substrate level Phosphorylation while electron transport makes its ATP through oxidative phosphorylation. Glycolysis and the Krebs cycle are important to electron transport; NADH carries electrons from glycolysis to the spot where electron transport takes place. NADH and FADH2 carry the electrons from the Krebs cycle to the spot of electron transport. So with out Glycolysis or the Krebs cycle electron transport would not take place.

The electron transport chain is located in the inner membrane of the mitochondrion. It is made up of a collection of molecules that are set up in a way that each molecule is less electronegative than the molecule below it. So like a set of stairs as you go down the stairs each molecule becomes more electronegative and then when you get to the second to last step if you have ever heard the saying, that last step is a big one you could use that phase in this context. The last step is from a relatively low electronegative molecule to a oxygen molecule which has a very high electro negativity. Most components of the chain are proteins. Tightly bound to these proteins are prosthetic groups, nonprotein essential for the catalytic functions of certain enzymes. During electron transport along the chain, these prosthetic groups alternate between reduced and oxidized states as they accept and donate electrons. Each member of the chain changes between a reduced state and an oxidized state. A component of the chain becomes reduced when it accepts electrons from its above stair (which has a lower affinity for the elections). Each member of the chain returns to its oxidized form as it passes electrons to the stair lower than it (which has a higher affinity for electrons) does. At the bottom is oxygen, the overall energy for electrons travailing from NADH to oxygen is 53 kcal/mol, but this fall is broken up in to a series of small steps by the electron transport chain.

Most of the ATP made from electron transport is from the electrons transported by the NADH from Glycolysis. There is another thing that adds to the amount of ATP that electron transport is the FADH2 from the Krebs cycle. FADH2 carries electrons from the Krebs cycle to the electron transport chain. It drops its electrons off at the third stair of the chain. The electron transport chain makes about one third less with FADH2 as the electron donor.

The electron transport chain makes no ATP directly. Its function is to ease the fall of electrons from food to oxygen, breaking a large free energy drop into a series of smaller steps that release energy in manageable amounts. The mitochondrion couple this electron transport and energy release to ATP synthesis this is called cheiosmosis. Populating the inner membrane of the mitochondria are many copies of the protein complex ATP synthase, this is the enzyme that actually makes ATP. It works like an ion pump but in the opposite direction. If you remember right on ion pump uses ATP as the energy source to run the pump. In the reverse of that process, an ATP synthase uses the energy of an existing ion gradient to power ATP synthase. The ion gradiant that drives oxidative phosphorylation is a proton gradient; that is, the power source for the ATP synthase is a difference in the concentration of protons on opposite sides of the inner mitochondrial membrane. We can also think of this gradient as a difference in pH, since pH is a measure of proton concentration. The chain is an energy converter that uses the exergonic flow of electrons to pump hydrogen across the membrane, from the matrix into the inter membrane space. The Hydrogen ions leak back across the membrane, diffusing down its gradient. But the ATP synthase, are the only patches of the membrane that are freely permeable to hydrogen ions. The complex of proteins functions as a mill that harnesses the exergonic flow of hydrogen ions to drive the phosphorylation of ADP. Thus, an hydrogen ion gradient couples the redox reactions of the electron transport chain to ATP synthesis. This coupling mechanism for oxidative phosphorylation is called chemiosmosis a term that highlights the relationship between chemical reactions and transport across a membrane.

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