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Lecture 30

Lecture 30. Pyruvate Oxidation and the Citric Acid Cycle. Aerobic Fate of Pyruvate: Overview. Mitochondria: Site of Oxidations. Pyruvate Oxidation to Acetyl-CoA. Pyruvate Dehydrogenase Complex. Complex enzyme 60 polypeptides of 3 kinds In mitocondrion matrix Regulated

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Lecture 30

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  1. Lecture 30 Pyruvate Oxidation and the Citric Acid Cycle

  2. Aerobic Fate of Pyruvate: Overview

  3. Mitochondria: Site of Oxidations

  4. Pyruvate Oxidation to Acetyl-CoA

  5. Pyruvate Dehydrogenase Complex • Complex enzyme • 60 polypeptides of 3 kinds • In mitocondrion matrix • Regulated • Inhibited by NADH and GTP • Stimulated by insulin

  6. Pyruvate Dehydrogenase Complex • Three enzymes and 5 coenzymes Total MW: 4.5 x 106! Also present: regulatory protein kinase, phosphatase

  7. Lipoic Acid: Acyl- and Redox Carrier

  8. Thiamine Pyrophosphate (TPP)

  9. Pyruvate Dehydrogenase Mechanism

  10. Pyruvate Dehydrogenase Mechanism

  11. Pyruvate Dehydrogenase Mechanism

  12. Pyruvate Dehydrogenase Mechanism

  13. Pyruvate Dehydrogenase Mechanism

  14. Pyruvate Dehydrogenase Mechanism

  15. Pyruvate Dehydrogenase Mechanism

  16. Pyruvate Dehydrogenase Mechanism

  17. PDH: The Overall Reaction • Acetyl-CoA enter Krebs cycle • NADH passes e– to O2

  18. Krebs Cycle Summary

  19. Importance of the Krebs Cycle 1. Central energy-yielding path 2. Point of convergence of catabolism of fats, CHO, protein 3. Source of precursors for biosynthesis

  20. Citrate Synthase: “Condensing Enzyme” ∆Gº= –32.2 kJ/mol

  21. Aconitase ∆Gº = +13.3 kJ/mol

  22. Isocitrate Dehydrogenase ∆Gº= –20.9 kJ/mol

  23. -Ketoglutarate Dehydrogenase Complex ∆Gº= –33.5 kJ/mol

  24. -Ketoglutarate Dehydrogenase Complex • Cofactors: FAD, NAD+, lipoate, TPP, CoASH • Mechanism  PDH complex

  25. Succinic Thiokinase ∆Gº= –2.9 kJ/mol

  26. Succinic Thiokinase • Multistep reaction:

  27. Nucleoside Diphosphate Kinase • Also uses • CTP • UTP • So NTPs are in equilibrium with each other ∆Gº= 0

  28. Succinate Dehydrogenase • Enzyme is membrane bound ∆Gº= 0

  29. Fumarase (Fumarate Hydratase) ∆Gº= –3.8 kJ/mol

  30. Malate Dehydrogenase ∆Gº= +29.7 kJ/mol [OAA] normally < 10-6 M

  31. Overall Reaction of Krebs Cycle

  32. Fate of NADH, FADH2ATP • Each NADH3 ATP • Each FADH22 ATP

  33. Energy Yield from Glucose Oxidation

  34. Citric Acid Cycle: Metabolic Hub

  35. Regulation of the Citric Acid Cycle

  36. Krebs Cycle in Motion Jon Maber Dept of Biochemistry and Molecular Biology The University of Leeds, UK http://bmbwww.leeds.ac.uk/designs/tcasteps

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