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Electron Transport Chain (Electron transport chain (The flow of electrons…
Electron Transport Chain
Electron transport chain
- The flow of electrons along the chain releases energy, which is used by complex I to pump protons through the intermembranal space.
- Two more electrons, donated from the hydrogen atoms of the reduced FAD molecule are accepted by complex II (making there four present electrons in total in complex II).
- The electrons of the reduced NAD are accepted by the first electron carrier, a protein complex called complex I, or reduced NAD hydrogenase, and the electrons are passed along the chain to the next carrier, complex II.
the fourth and final stage of aerobic respiration involves electron carriers in the inner mitochondrial membrane, called cytochromes. These membranes are folded into cristae so that there is a larger surface area. The chain of electron carriers is called the electron carrier chain.
- The molecules of reduced FAD and NAD are reoxidised by donating their two hydrogen atoms to the electron carriers. One hydrogen atom is split One hydrogen atom is split into one proton and one electron, so each reduced NAD and FAD donates two electrons and two protons.
- These now four electrons are passed along to complex III (transported by a coenzyme called coenzyme-Q), which releases energy - although this is not used by complex II to pump a proton, as complex II can't pump protons.
- The four electrons are accepted in pairs by complex III, when they are again transported along to complex IV (using the coenzyme cytochrome c), and the energy released is used to pump a proton through the internal membrane space.
- The four electrons are then donated one-by-one to molecular oxygen, which also accepts four protons - two from the reoxidised FAD molecule, and two which are pumped back through the membrane using the enzyme at the end of the electron transport chain, to form water, a waste product.
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Chemiosmosis
The protons are transported through ion channels which are embedded in the membrane, which are associated with the ATP synthase enzyme. This flow of protons is called chemiosmosis.
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Evidence from studies
Researchers treated isolated mitochondria by placing them in solutions of very low water potential so that the outer membrane ruptured, releasing the contents of the intermembrane space.
By further treating the resulting mitoblasts they could rupture the inner membrane, releasing the matrix contents. This allowed researchers to find out that the link reaction and the Krebs cycle took place in the matrix.
Products
Before the electron transport chain occurs, there is a net production of 2 ATP molecules during glycolysis and two ATP during the Krebs cycle per molecule of glucose. 10 reduced NAD and 2 reduced FAD are also made.
Because, during the previous stages of aerobic respiration, 10 reduced NAD are produced, that should 25 ATP molecules of ATP during oxidative phosphorylation.