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Electron transport chain & oxidative phosphorylation
- 1. ELECTRON TRANSPORT CHAIN &OXIDATIVE PHOSPHORYLATION PRESENTED BY; ISMA ZULFIQAR
- 2. OVERVIEW • Electron transportand oxidative phosphorylation re-oxidize NADH and FADH2 and trap the energy released as ATP. • In eukaryotes, electron transport and oxidative phosphorylation occur in the inner membrane of mitochondria whereas in prokaryotes the process occurs in the plasma membrane.
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- 4. ELECTRON TRANSPORT CHAIN •This is the final common pathway in aerobic cells by which electrons derived from various substrates are transferred to oxygen. Electron transport chain (ETC) is a series of highly organized oxidation-reduction enzymes. • The inner membrane transport only specific substances such as ATP, ADP, pyruvate, succinate, α-ketoglutarate, malate and citrate etc. The enzymes of the electron transport chain are embedded in the inner membrane in association with the enzymes of oxidative phosphorylation.
- 5. COMPLEX OR COMPONENTSOF ETC • The electron transport chain in the mitochondrial membrane has been separated in 4 (four) complexes from Complex I-IV. • Complex I, also called NADH ubiquinone oxidoreductase or NADH dehydrogenase, is a large enzyme composed of 42 different polypeptide chains. High-resolution electron microscopy shows Complex I to be L-shaped, with one arm of the L in the membrane and the other extending into the matrix.
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- 7. COMPLEX II Succinate toubiquinone • It is smaller and simpler than Complex I. • Flow of electrons from succinate to CoQ occurs via FADH2 • It does not pump protons across the mitochondrial membrane, hence this protein complex does not contribute to proton gradient that lead to ATP production.
- 8. COMPLEX III UBIQUINONE TOCYTOCHROME C • The transfer of electrons from ubiquinol (QH2) to cytochrome c. • Functions as i. Proton pump, and ii. Catalyze transfer of electrons It is believed that 4 (four) protons are pumped across the mitochondrial membrane during the oxidation.
- 9. COMPLEX IV CYTOCHROME CTO O2 • Complex IV, also called cytochrome oxidase, carries electrons from cytochrome c to molecular oxygen, reducing it to H2O. • This is the terminal component of ETC. It catalyses the transfer of electrons from Cyt-c to molecular O2 via Cyt-a, Cu++ ions and Cyt- a3.
- 10. Summary of theflow of electrons and protons through the four complexes of the respiratory chain
- 12. PROTON-MOTIVE FORCE • Foreach pair of electrons transferred to O2, four protons are pumped out by Complex I, four by Complex III, and two by Complex IV. This introduces proton motive force. • The proton-motive force, has two components: I. The chemical potential energy due to the difference in concentration of a chemical species (H) in the two regions separated by the membrane. II. The electrical potential energy that results from the separation of charge when a proton moves across the membrane.
- 13. OXIDATIVE PHOSPHORYLATION • Thechemiosmotic model, proposed by Peter Mitchell, is the paradigm for this mechanism. • According to chemiosmotic theory applied to mitochondria, electrons from NADH and other oxidizable substrates pass through a chain of carriers arranged asymmetrically in the inner membrane. Electron flow is accompanied by proton transfer across the membrane, producing both a chemical gradient and an electrical gradient. • The inner mitochondrial membrane is impermeable to protons, protons can reenter the matrix only through proton-specific channels. The proton-motive force that drives protons back into the matrix provides the energy for ATP synthesis.
- 15. What would happento the energy stored in the proton gradient if not used to synthesize ATP or other cellular work? • It would be released as heat, and interestingly enough, some types of cells deliberately use the proton gradient for heat generation rather than ATP synthesis. This might seem wasteful, but it's an important strategy for animals that need to keep warm. • Hibernating mammals (such as bears) have specialized cells known as brown fat cells. In the brown fat cells, uncoupling proteins are produced and inserted into the inner mitochondrial membrane. These proteins are simply channels that allow protons to pass from the intermembrane space to the matrix without traveling through ATP synthase. By providing an alternate route for protons to flow back into the matrix, the uncoupling proteins allow the energy of the gradient to be dissipated as heat.
- 16. ATP YIELD • Oxidative phosphorylation producesmost of the ATP made in aerobic cells. Complete oxidation of a molecule of glucose to CO2 yields 30 or 32 ATP.
- 17. REFERENCES • https://www.khanacademy.org/science/ap-biology/cellular energetics/cellular-respiration-ap/a/oxidative- phosphorylation-etc • LehningerPrinciples of Biochemistry, 6th edition. • Instant Notes in Biochemistry, 4th eidition. • Textbook of medical biochemistry by MN chatterjea, 8th edition.