The mitochondrion has the ability to use the electron transport to create an electrochemical proton gradient during biochemical reactions in the body. However, the process involves membrane-based energy-conversion activities. Therefore, the mitochondria use the chemiosmotic mechanisms with the help of the chloroplasts, archea, and bacteria.
How the energy of the electron is used to create a proton gradient
Protons move across membranes through the mechanism similar to that of Na+ and K+ and the protons in water are highly mobile and flickering. Therefore, they can move freely in the hydrogen-bonded network within the water molecules through rapid dissociation and the ability to associate water molecules with their neighbors. The mechanism facilitates the movement of electrons across a protein pump that is embedded in a lipid bilayer. Electrons are then passed along the electron-transport chain that forces protons to move to one side and causes the rearrangement of electron carriers (Lumen, n.d). Compounds that contain the highest number of redox potentials develop the weakest affinity for electrons; hence, they will donate the largest quantity of electrons. Free-energy drop ensures that the reaction continues with explosive force and release energy in the form of heat. The NADH and FADH2 that are formed during glycolysis and fatty acid oxidation contain a pair of electrons with high transfer potential and have the ability to reduce molecular oxygen to water (Astakhova, et al., 2019). The process generates large amounts of free energy that is used to produce ATP. Consequently, more ATP is formed during electron transfer to and O2 is eventually produced through a series of electron carriers (Ramsay, 2019). As noted above, the mitochondria are the major sources of ATP, particularly in aerobic organisms. In the process, oxidative phosphorylation produces between 26 and 30 molecules of ATP following the complete oxidation of glucose to CO2 and H2O (Elmore & Merrill, 2019; Xu, et al., 2019). Generally, the NADH and FADH2 are useful in regenerating electron carriers. They pass electrons to the electron transport chain and initiate their conversion into NAD+ and FAD (Ahern, n.d). Consequently, the oxidized form of the electron carriers is useful in glycolysis and the citric acid cycle to maintain the running of the processes that lead to the proton gradient. The gradient finally forms when the protein chain builds a proton gradient across the inner membranes of the mitochondria, which develop higher concentrations of H+ (Khan Academy, 2020). Every enzyme complex that is responsible for respiratory processes doubles the energy released during electron transfer across it and facilitates electron transfer from water within the mitochondrial matrix (Lecture Notes, n.d). In the process, some electrons are released from the other side of the membrane and they enter the intramembranous space. The flow of electrons along the electron-transport chain results in pumping actions that drive protons that exist across the membrane out of the matrix (Zhang & Li, 2019). The resultant effect is the creation of electrochemical protons across the inner membrane.
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How is a proton gradient used to phosphorylate ADP?
The proton gradient so created reduces through chemiosmotic coupling and this increases the pumping rate of the respiratory chain, leading to more protons entering the inner membrane of the mitochondria. The constant supply of electrons in the respiratory chain increases both respiration and ATP synthesis (Georgia Tech Biology, n.d). The process stimulates mitochondrial matrix dehydrogenase and increases the supply of electrons to the respiratory chain. This increases the respiration rate and doubles the synthesis of ATP. The metabolic rate of the mitochondria changes and respiration reduces while proton electrochemical gradient increases (Wilson, 2017). At this initial stage, there is no ATP synthesis. As respiration increases, the proton electrochemical gradient reduces and protons start leaking through the inner membrane of the mitochondria.
References
Ahern, K. (n.d). Electron Transport & Oxidative Phosphorylation. http://oregonstate.edu/instruct/bb451/451material/Keynotes/28ETSOxidativePhosphorylation.pdf
Astakhova, A., et al. (2019). Inhibitors of Oxidative Phosphorylation Modulate Astrocyte Inflammatory Responses through AMPK-Dependent Ptgs2 mRNA Stabilization. Cells, 8, 1185. https://www.mdpi.com/2073-4409/8/10/1185/pdf
Elmore, S. E. & Merrill, M. A. (2019). Oxidative Phosphorylation Impairment by DDT and DDE. Front. Endocrinol . https://www.frontiersin.org/articles/10.3389/fendo.2019.00122/full
Georgia Tech Biology. (n.d). Biology 1510 Biological Principles. Word press. http://bio1510.biology.gatech.edu/module-3-molecules-membranes-and-metabolism/05-respiration-chemiosmosis-and-oxidative-phosphorylation-2/
Khan Academy. (2020). Oxidative phosphorylation. https://www.khanacademy.org/science/biology/cellular-respiration-and-fermentation/oxidative-phosphorylation/a/oxidative-phosphorylation-etc
Lecture Notes (n.d). Electron Transport Generates a Proton Gradient Across the Membrane. http://home.ku.edu.tr/~okeskin/Biol200/lecture10-biol.pdf
Lumen. (n.d). Biology for Majors I. Module 6: Metabolic Pathways. Electron Transport Chain. Lumen WayMaker. https://courses.lumenlearning.com/wm-biology1/chapter/reading-electron-transport-chain/
Ramsay, R. R. (2019). Electron carriers and energy conservation in mitochondrial respiration. ChemTexts , volume 5, Article number: 9. Springer. https://link.springer.com/article/10.1007/s40828-019-0085-4
Wilson, D. F. (2017). Oxidative phosphorylation: regulation and role in cellular and tissue metabolism. The Journal of Psychology , Volume 595, Issue 23. https://physoc.onlinelibrary.wiley.com/doi/full/10.1113/JP273839
Xu, Y., et al. (2019). Assembly of the complexes of oxidative phosphorylation triggers the remodeling of cardiolipin. New York: New York University School of Medicine. https://www.pnas.org/content/pnas/early/2019/05/17/1900890116.full.pdf
Zhang, X. C. & Li, B. (2019). Towards understanding the mechanisms of proton pumps in Complex-I of the respiratory chain. Biophysics Reports , volume 5, pages 219–234. Springer. https://link.springer.com/article/10.1007/s41048-019-00094-7
