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Stage 4: Electron Transport and Chemiosmosis

Stage 4: Electron Transport and Chemiosmosis. Angel Gu , Samantha Wong, Linda Yang, Angel Zhang. What is the electron transport chain?.

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Stage 4: Electron Transport and Chemiosmosis

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  1. Stage 4: Electron Transport and Chemiosmosis Angel Gu, Samantha Wong, Linda Yang, Angel Zhang

  2. What is the electron transport chain? A chain of protein complexes embedded in the inner mitochondrial membrane. Transports electrons and pumps hydrogen ions into the intermembrane space to create a gradient.

  3. Components of the electron transport chain (ETC) • NADH dehydrogenase • Ubiquinone (Q) • Succinate dehydrogenase • Cytochrome b-c1 • Cytochrome c • Cytochrome oxidase • Arranged in order of increasing electronegativity (weakest to strongest)

  4. NADH produced from Krebs cycle VS NADH produced from glycolysis • NADH produced in the cytoplasm by glycolysis: CAN diffuse from outer mitochondrial membrane to intermembrane space. CANNOT diffuse from inner membrane to matrix. VS • NADH produced from Krebs cycle: Already in the matrix.

  5. What to do? • Cytosolic NADH (NADH that are produced by glycolysis) • Pass electrons to shuttles • Glycerol-phosphate shuttle: Transfers electrons from cytosolic NADH to FAD to produce FADH2 • Aspartate shuttle: Transfers electrons from cytosolic NADH to NAD+to produce NADH

  6. Complex I: NADH dehydrogenase • NADH dehydrogenase oxides NADH back to NAD+ • The electrons are transferred to flavin mononucleotide (FMN) which reduces to FMNH2 • The electrons are then passed to iron-sulphur proteins (FeS) located in NADH dehydrogenase NADH + H+ NAD+ + 2H+ + 2e- FMN + 2H+ + 2e-  FMNH2

  7. Complex I Continued… • Electrons are accepted by Fe3+ which is reduced to Fe2+ • These two electrons are then given to ubiquinone (Q) • The two hydrogen ions are pumped into the intermembrane space 2Fe3+ + 2e- 2Fe2+ *One hydrogen ion is pumped per electron transferred

  8. Ubiquinone (Q) • A mobile electron carrier • Carries electrons to complex III, cytochrome b-c1 2Fe2+ gives 2e- to Q Q is reduced to QH2 (ubiquinol) and 2Fe2+ is oxidized 2Fe3+

  9. Interactive Animation: http://www.brookscole.com/chemistry_d/templates/student_resources/shared_resources/animations/oxidative/oxidativephosphorylation.html

  10. Complex II: Succinate Dehydrogenase • oxidation of succinate from Krebs cycle to fumarate • FADH2 then tries to oxidize back into FAD by passing its electrons to 2Fe3+, which is reduced to 2Fe2+ (Like in Complex 1) Succinate + FAD Fumarate + FADH2 2Fe3+ + 2e- 2Fe2+

  11. Complex II Continued... • These electrons from 2Fe2+ are then stolen by ubiquinone (Q), which carries them to complex III. • *Unlike complex I, complex II doesn’t have enough free energy for active transport of the hydrogen ions (protons) from FADH2 across the intermembrane . This is why oxidation of FADH2 only yields 2 ATP molecules instead of 3 ATP molecules like NADH. Q + 2Fe2+  2Fe3+ + QH2

  12. Complex III: cytochrome b-c1 • Contains cytochrome b, cytochrome c1, and FeS proteins. • QH2 passes two electrons to cytochrome b causing Fe3+ to reduce to Fe2+ • Same way from cyt b to FeS protein and then to cyt c1

  13. Cytochrome C (c) • I’m a protein and like Q... • I am also a water soluble mobile electron carrier. I transport electrons one at a time from complex III to complex IV.

  14. Complex IV: Cytochrome Oxidase (The End of the Line) • This is the end of the line for electrons from NADH or succinate. • Oxygen (breathed in) is reduced and when combined with these electrons, they form... WATER THIS REACTION IS EXPLOSIVE! It’s highly exergonic, releasing large amounts of energy. ½ O2 (g) + 2H+ + 2e-  H2O (l)

  15. Electrochemical gradient • A concentration gradient created by pumping ions into a space surrounded by a membrane that is impermeable to the ions. • Two components: electrical and chemical • Proton-motive force (PMF) moves protons through an ATPase complex on account of the free energy stored in the form of an electrochemical gradient of protons across a biological membrane.

  16. Chemiosmosis • Peter Mitchell – Nobel Prize in Chemistry in 1978 • A process for synthesizing ATP using the energy of an electrochemical gradient and the ATP synthase enzyme. • “osmosis” • After chemiosmosis, ATP molecules are transported through both mitochondrial membranes.

  17. Connections! • Electrons from NADH and FADH2 were passed down the ETC • As the electrons move down, energy released moves protons to create electrochemical gradient • Protons move through proton channels, and release energy to synthesize ATP from ADP and Pi • The many processes of ATP synthesis are all continuous

  18. Respiration • C6H12O6 + 6O2 6H2O + 6CO2 • The oxygen is necessary to take away the electrons from the ETC so the new electrons can keep flowing. Only oxygen is electronegative enough • The ETC cannot get clogged up by electrons • Oxygen takes two electrons and two protons from the matrix, and forms water • Glucose provides electrons and energy in its bonds for the body.

  19. Oxidative Phosphorylation • Each step of ATP synthesis is completely dependent on its previous step • Glycolysis  Pyruvate Oxidation  The Krebs Cycle  Electron Transport Chain and Chemiosmosis • Each step depends on the step before for the correct molecules and energy to work

  20. Bibliography • Highered Mcgraw Hill. Electron Transport System and ATP Synthesis. October 26, 2011. <http://highered.mcgrawhill.com/olcweb /cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/1200 71/bio11.swf::Electron%20Transport%20System%20and%20ATP%20S ynthesis> • Interactive Animations. Oxidative Phosphorylation. October 26, 2011. <http://www.wiley.com/college/boyer/0470003790/animations/elec tron_transport/electron_ transport.htm> • Leeds Lecture. Electron Transport Chain. October 26, 2011. <http://www.dentistry.leeds.ac.uk/biochem/lecture/etran /etran.htm> • Nelson Biology 12. Chapter 2 Cellular Respiration. Pages 103-108.  • Thomson Brooks/Cole. The Mitochondrion. October 26, 2011. <http://www.brookscole.com/chemistry_d/templates/student_resou rces/shared_resources/animations/oxidative/oxidativephosphorylatio n.html>

  21. Bibliography continued… • Brooks, Dr. S. J.. "Electron Transport Chain." University of Leeds. N.p., n.d. Web. 19 Oct. 2011. <www.dentistry.leeds.ac.uk/biochem/lecture /etran/etran.htm>. • Carlson, Rebecca. "Hey Soul Sister/Electron Transport Chain." YouTube. N.p., n.d. Web. 18 Oct. 2011. <http://www.youtube.com/watch?v =DNReloT3QYU>.  • Cengage. "Oxidative Phosphorylation." Thomson Books. N.p., n.d. Web. 18 Oct. 2011. <www.brookscole.com/chemistry_d/templates /student_resources/shared_resources/animations/oxidative/oxidativ ephosphorylation.html>. • Khan Academy. "Electron Transport Chain." YouTube. N.p., n.d. Web. 18 Oct. 2011. <http://www.youtube.com/watch?v=mfgCcFXUZRk>. • Wiley, John. "Concepts in Biochemistry - Interactive Animations." Wiley College . N.p., n.d. Web. 19 Oct. 2011. <http://www.wiley.com/college/boyer/0470003790/animations/elec tron_transport/electron_transport.htm>. 

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