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Chapter 7

Chapter 7. Biological Oxidation. Biological oxidation is the cellular process in which the organic substances release energy (ATP), produce CO2 and H2O through oxidative-reductive reactions. organic substances : carbohydrate, fat and protein. 7.1 Principal of Redox Reaction.

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Chapter 7

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  1. Chapter 7 Biological Oxidation

  2. Biological oxidation is the cellular process in which the organic substances release energy (ATP), produce CO2 and H2O through oxidative-reductive reactions. organic substances: carbohydrate, fat and protein

  3. 7.1 Principal of Redox Reaction The electron-donating molecule in a oxidation-reduction reaction is called the reducing agent or reductant; the electron-accepting molecule is the oxidizing agent or oxidant:for example: Fe2+ (ferrous) lose -e Fe3+ (ferric) gain +e

  4. Several forms of Biological Oxidation Redox reaction = reduction-oxidation reaction Several forms of Biological Reduction 1. Loss of electrons 2. Dehydrogenation 3. Oxygenation 1. Gain of electrons 2. Hydrogenation 3. Deoxygenation

  5. oxidation-reduction potential ( or redox potential), E : it is a measure of the affinity of a substance for electrons. It decide the loss (or the gain) of electrons. • A positive E: the substance has a higher affinity for electrons , accept electrons easily. • A negative E: the substance has a lower affinity for electrons , donate electrons easily.

  6.  E0`, the standard redox potential for a substance :is measured under stander condition(25℃, 1mmol/L reaction substance),at pH7, and is expressed in volts.

  7. Section 7.2 Respiration Chain and Oxidative Phosphorylation

  8. 7.2.1 Respiratory Chain • Term: A chain in the mitochondria consists of a number of redox carriers for transferring electrons from the substrate to molecular oxygen to form oxygen ion, which combines with protons to form water.

  9. Redox carriersincluding 4 protein complexes 1.Complex I: NADH:ubiquinoneoxidoreductase NADH:CoQ oxidoreductase 2.Complex II: Succinatedehydrogenase 3.Complex III: cytochrome bc1(ubiquinone Cyt coxidoreductase) 4.Complex IV: cytochrome oxidase

  10. complex Ⅰ NADH→ →CoQ FMN; Fe-SN-1a,b;Fe-SN-4;Fe-SN-3; Fe-SN-2 Complex I (NADH:ubiquinoneoxidoreductase) • Function: transfer electrons from NADH to CoQ • Components: NADH dehydrogenase (FMN) Iron-sulfur proteins (Fe-S)

  11. R=H: NAD+; R=H2PO3:NADP+ 1.NAD(P)+:NicotinamideAdenineDinucleotidePhosphate)

  12. Oxidation of NADH is a 2-electron(2e), 2-proton(2H) reaction NAD+ or NADP+ NADH or NADPH

  13. 2. FMN can transfer 1 or 2 hydride ions each time FMN: flavin mononucleotide Accepts 1 H+ and 1 e- to form semiquinone = stable free radical Accepts 2 H+ and 2 e- to give fully reduced form

  14. 3. Iron-sulfur clusters (Fe-S) transfers 1-electron at a time, without proton involvedFe3++e- Fe2+

  15. 4.Ubiquinone (CoQ) is lipid-soluble, not a component of complex Ⅰ,can transfer 1 or 2 hydride ions each time.Function:transfer electrons and protons from complex Ⅰ,Ⅱto complex Ⅲ.

  16. Reduced Fe-S NADH+H+ FMN Q NAD+ FMNH2 Oxidized Fe-S QH2 Matrix Intermembrane space

  17. Complex Ⅱ Succinate→ →CoQ Fe-S1;b560;FAD;Fe-S2 ;Fe-S3 Complex II:Succinatedehydrogenase (Succinate: CoQ oxidoreductase) • Function: transfer electrons from succinate to CoQ • Components: Succinatedehydrogenase (FAD, Fe-S) Cytochrome b560

  18. Cytochromes a, b, c are heme proteins, their heme irons participate redox reactions of e- transport. Fe3++e- Fe2+

  19. Intermembrane space Matrix Succinate

  20. complex Ⅲ QH2→ →Cyt c b562; b566; Fe-S; c1 Complex III:cytochrome bc1(ubiquinone Cyt coxidoreductase) • Function: transfer electrons from CoQ to cytochrome c • Components: iron-sulfur protein cytochrome b(b562, b566) cytochrome c1

  21. Cytochromec is soluble, which will transfer electrons to complex Ⅳ Intermembrane space Matrix

  22. Complex IV Cyt c → → O2 CuA→a→a3→CuB Complex IV:cytochrome oxidase • Function: transfer electrons from Cyt c to molecule oxygen, the final electron acceptor. • Components: cytochrome aa3 copper ion (Cu2+) Cu2+ + e- Cu+

  23. Cytochrome c Coenzyme Q ubiquinone/ol

  24. Sequence of respiratory chain Principles: • e- tend to flow from a redox pair with a lower E°to one with a higher E° • In the e--transport chain, e--carriers are arranged in order of increasing redox potential, making possible the gradual release of energy stored in NADH, FADH2

  25. Redox potential redox pair E0

  26. There are two respiratory chains • NADH respiratory chain NADH Complex Ⅰ CoQ Complex Ⅲ cytochrome c Complex Ⅳ O2 • Succinate (FADH2) respiratory chain Succinate ComplexⅡ CoQ ComplexⅢ cytochrome c ComplexⅣ O2

  27. FADH2 respiration chain NADH respiration chain

  28. 7.2.2 Oxidative Phosphorylation • The oxidation of organic nutritions produces the energy-rich molecules, NADH and FADH2. • The oxidation of NADH or FADH2 in mitochondrial is the electron transferring through respiration chain. • The free energy produced in electron transferring supports the phosphorylation of ADP to form ATP. • The oxidation of NADH or FADH2 and the formation of ATP are coupled process, called Oxidation Phosphorylation.

  29. The Chemiosmotic Theory • The free energy of electron transport is conserved by pumping protonsfrom the mitochondrial matrix to the intermembrane space so as tocreate an electrochemical H+ gradient across the inner mitochondrialmembrane. The electrochemical potential of this gradient is harnessedto synthesize ATP. Peter Mitchell

  30. Electrochemical H+ gradient (Proton-motive force) 2 components involved 1. Chemical potential energy due to difference in [H+] in two regions separated by a membrane 2. Electrical potential energy that results from theseparation of charge when a proton moves across the membrane without a electron.

  31. Complex I: 4 H+ expelled pere--pair transferred to Q Complex III: 4 H+ expelled per e--pair transferred to Cyt c Complex IV: 2e- + 2 H+ from matrixconvert ½ O2 to H2O; 2 further H+expelledfrom matrix

  32. Proton pumping:Reduction-dependentconformational switch ofan e--transport complex Conformation 1 (high affinity for H+) Conformation 2 (low affinity for H+).

  33. ATP Synthase Inner Membrane Intermembrane space (ab2c9-12) (α3β3γδε) Matrix C ring

  34. β-subunit take up ADP and Pi to form ATP ADP + Pi ATP Each of 3 b-subunits contains an active site F1: multisubunit complex that catalyzes ATP synthesis F0 = proton-conducting transmembrane unit

  35. When protons flow back through F0 channel, γ-subunit is rotated by the rotation of c ring, then the conformations of β-subunits are changed, this lead to the synthesis and release of ATP. To form a ATP need 3 protons flow into matrix. H+ flow β-subunit has three conformations:T (tight), L (loose), O (open)

  36. H+ ADP3- ATP4- H2PO4- H+ 胞液侧 F0 基质侧 F1 H2PO4- H+ ADP3- H+ Translocation of ATP , ADP and Pi. ADP3- H2PO4- Intermembrane space Matrix ATP4-

  37. P/O ratios • P/O ratio is the rate of phosphate incorporated into ATP to atoms of O2 utilized. It measure the number of ATP molecules formed per two electrons transfer through the respiratory chain. • NADH respiratory chain : 2.5, • FADH2 respiratory chain: 1.5

  38. During two electrons transfer through NADH respiratory chain, ten protons are pumped out of the matrix. • To synthesis and translocation an ATP, four protons are needed. • So, two electrons transport can result in 2.5 ATP. • To succinate respiratory chain , two electrons transport can result in 1.5 ATP.

  39. Regulation of Oxidative Phosphorylation • 1.PMF (proton motive force) regulate the electron transport. higher PMF lower rate of transport • 2.ADP concentration resting condition: energy demanded is low, ADP concentration is low, the speed of Oxidative Phosphorytion is low. active condition: the speed is high.

  40. Inhibitor of Oxidative Phosphorylation • 1.Inhibitor of electron transport Succinate Cyanide, Azide Antimycin A Carbon Monoxide × × × Retonone Amytal

  41. H+ Cyt c Ⅳ Ⅱ Ⅰ F0 F1 ADP+Pi ATP H+ • 2.Uncoupling agents uncoupling protein (in brown adipose tissue), 2,4-dinitrophenol, Pentachlorophenol heat Intermenbran space uncoupling protein H Q Ⅲ Matrix + H+ 2,4-dinitrophnol

  42. 3.Oligomycin bonds at the connection of F0 and F1, inhibit the function of ATP synthase. Intermembrane space Oligomycin Matrix C ring

  43. Succinate Ⅱ Retonone Amytal Antimycin A × × × Ⅳ Ⅰ Ⅲ × Oligomycin Uncoupling agent × Ⅴ

  44. ATP and other Energy-rich compounts ATP has two energy-rich phosphoric acid anhydride bonds, the hydrolysis of each bond release more energy than simple phosphate esters. ～ ～

  45. Some Energy-rich compounds ΔGº’ Structure Exemple creatine phosphate phosphoenolpyruvate acetylphosphate Acetyl CoA

  46. The hydrolysis of energy-rich bond: ΔGº’ = -5～-15kcal/mol • The compounds with energy-rich bond are high-energy compounds. • The hydrolysis of low-energy bond: ΔGº’ = -1～-3kcal/mol • The compounds with low energy bond are low-energy compounds.

  47. Transport of high-energy bond energies • 1.Substrate level phosphorylation Glycerate 1,3-biphosphate + ADP Glycerate 3-phosphate +ATP ΔGº’ = -4.5kcal/mol Phosphoenolpyruvate +ADP Pyruvate + ATP ΔGº’ = -7.5kcal/mol

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