GMA Biology
organized (not written) by Julie Thompson Seal coachjulieseal@yahoo.com
Kreb Cycle and the Electron Chain Transport
Electron transport chains in mitochondria[edit]
Most eukaryotic cells have mitochondria, which produce ATP from products of the citric acid cycle, fatty acid oxidation, and amino acid oxidation. At the mitochondrial inner membrane, electrons fromNADH and succinate pass through the electron transport chain to oxygen, which is reduced to water. The electron transport chain comprises an enzymatic series of electron donors and acceptors. Each electron donor passes electrons to a more electronegative acceptor, which in turn donates these electrons to another acceptor, a process that continues down the series until electrons are passed to oxygen, the most electronegative and terminal electron acceptor in the chain. Passage of electrons between donor and acceptor releases energy, which is used to generate a proton gradient across the mitochondrial membrane by actively “pumping” protons into the intermembrane space, producing a thermodynamic state that has the potential to do work. The entire process is called oxidative phosphorylation, since ADP is phosphorylated to ATP using the energy of hydrogen oxidation in many steps.
A small percentage of electrons do not complete the whole series and instead directly leak to oxygen, resulting in the formation of the free-radical superoxide, a highly reactive molecule that contributes to oxidative stress and has been implicated in a number of diseases and aging.
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Chemically, ATP is an adenine nucleotide bound to three phosphates.
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There is a lot of energy stored in the bond between the second and third phosphate groups that can be used to fuel chemical reactions.
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When a cell needs energy, it breaks this bond to form adenosine diphosphate (ADP) and a free phosphate molecule.
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In some instances, the second phosphate group can also be broken to form adenosine monophosphate (AMP).
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When the cell has excess energy, it stores this energy by forming ATP from ADP and phosphate.
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ATP is required for the biochemical reactions involved in any muscle contraction. As the work of the muscle increases, more and more ATP gets consumed and must be replaced in order for the muscle to keep moving.
Because ATP is so important, the body has several different systems to create ATP. These systems work together in phases. The interesting thing is that different forms of exercise use different systems, so a sprinter is getting ATP in a completely different way from a marathon runner!