10 oxidative phosphorylation 2014-2015
DESCRIPTION
HKU science lecture notesTRANSCRIPT
![Page 1: 10 Oxidative Phosphorylation 2014-2015](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4f31a28ab9b02a36b5f/html5/thumbnails/1.jpg)
Oxidative Phosphorylation
- Glycolysis + TCA cycle produces very little ATP directly (substrate level): Glycolysis – 2 ATPs and TCA cycle – 2 ATPs per glucose
- The rest of the energy is stored in the reduced cofactors: 10 NADH + 2 FADH2 per glucose
- Oxidation of the reduced co-factors releases energy:
(G' = -220 kcal/mol)
(G' = -182 kcal/mol)
- Consider that: C6H12O6 + 6 O2 6 CO2 + 6 H2O (G' = -2870 kcal/mol)
FADH2 + 1/2 O2 FAD + H2O
NADH + H+ + 1/2 O2 NAD+ + H2O
- Thus, the reduced co-factors from oxidation of 1 mole of glucose store 10 X 220 + 2 X 182 = 2564 kJ of energy, accounting for about 90% of the total realizable energy (under standard conditions)
![Page 2: 10 Oxidative Phosphorylation 2014-2015](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4f31a28ab9b02a36b5f/html5/thumbnails/2.jpg)
NAD+/NADH and NADP+/NADPH
- Diffusible 2 electron carriers - Accept or donate 1 hydride (H-) ion (1 proton and 2 electrons)
![Page 3: 10 Oxidative Phosphorylation 2014-2015](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4f31a28ab9b02a36b5f/html5/thumbnails/3.jpg)
FAD/FADH2 and FMN/FMNH2 - Bound in enzymes as prosthetic groups - 2 electron-carriers - May transfer 1H+ + 1e- at a time
![Page 4: 10 Oxidative Phosphorylation 2014-2015](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4f31a28ab9b02a36b5f/html5/thumbnails/4.jpg)
![Page 5: 10 Oxidative Phosphorylation 2014-2015](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4f31a28ab9b02a36b5f/html5/thumbnails/5.jpg)
The mitochondrion - Aerobic oxidation of biomolecules
Alligator jaw muscle - white muscle Flight muscle - red muscle
![Page 6: 10 Oxidative Phosphorylation 2014-2015](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4f31a28ab9b02a36b5f/html5/thumbnails/6.jpg)
Electron transport chain (ETC) in mitochondria
Four integral membrane protein complexes:
Electron transfer reactions
- The driving force is expressed as a difference in the standard redox potentials of the components, and this is equivalent to the change in free energy:
G’ = -nF E' n = no. of e- transferred F = 96.4 kJ mol-1 V-1
E‘ = EA' - ED'
- Electron flow is favorable from donors of low potential (i.e. more negative E values) to acceptors of high potential.
![Page 7: 10 Oxidative Phosphorylation 2014-2015](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4f31a28ab9b02a36b5f/html5/thumbnails/7.jpg)
Complex I
Complex II Complex III Complex IV
![Page 8: 10 Oxidative Phosphorylation 2014-2015](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4f31a28ab9b02a36b5f/html5/thumbnails/8.jpg)
![Page 9: 10 Oxidative Phosphorylation 2014-2015](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4f31a28ab9b02a36b5f/html5/thumbnails/9.jpg)
![Page 10: 10 Oxidative Phosphorylation 2014-2015](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4f31a28ab9b02a36b5f/html5/thumbnails/10.jpg)
NADH dehydrogenase (Complex I)
• Cofactors (electron carriers): riboflavin coenzyme FMN, iron-sulfur clusters, • transfers electrons from NADH to unbound ubiquinone (Q) • the unbound ubiquinol (QH2) carries electrons diffuses through inner membrane to cytochrome bc1 complex (Complex III)
Overall: NADH + H+ + Q NAD+ + QH2
Proton pumping
(matrix)
(intermembrane space)
![Page 11: 10 Oxidative Phosphorylation 2014-2015](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4f31a28ab9b02a36b5f/html5/thumbnails/11.jpg)
FMN
- Protein-bound co-factor - Accepts/donates 1 hydride ion
(1 electron + 1 proton) at a time - 2 electron-carrier
![Page 12: 10 Oxidative Phosphorylation 2014-2015](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4f31a28ab9b02a36b5f/html5/thumbnails/12.jpg)
Single electron carriers: Fe2+ Fe3+ + e-
4Fe-4S: 2Fe-2S:
- only the inorganic S is counted in the designation - each Fe is always coordinated by 4 S - 4 cysteine residues from the protein also contribute 4S to the cluster - it is also posible to have a single Fe coordinated by 4 cysteine residues
Iron-sulfur (Fe-S) clusters
Protein
Protein
![Page 13: 10 Oxidative Phosphorylation 2014-2015](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4f31a28ab9b02a36b5f/html5/thumbnails/13.jpg)
Q (or CoQ)/QH2
- Diffusible through inner membrane
- Accepts/donates 1 electron + 1 proton at a time
- A carrier of both electrons (2) and protons (2)
![Page 14: 10 Oxidative Phosphorylation 2014-2015](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4f31a28ab9b02a36b5f/html5/thumbnails/14.jpg)
• The only membrane-bound enzyme in TCA cycle • Contains an internal chain of electron transfer cofactors • No proton pumping in Complex II
Succinate dehydrogenase (Complex II)
(matrix)
(intermembrane space)
![Page 15: 10 Oxidative Phosphorylation 2014-2015](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4f31a28ab9b02a36b5f/html5/thumbnails/15.jpg)
![Page 16: 10 Oxidative Phosphorylation 2014-2015](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4f31a28ab9b02a36b5f/html5/thumbnails/16.jpg)
Cytochrome bc1 complex (Complex III) • Electron carriers: Fe-S clusters, cytochrome b and cytochrome c1
• Transfers electrons from ubiquinone to cytochrome c
• QH2 + 2 cyt c1 (oxidized) + 2 H+ Q + 2 cyt c1 (reduced) + 4H+
• Cytochrome c is a water-soluble protein coenzyme in the intermembrane space.
• Complex III pumps 4 protons per 2 electrons transferred
(Iron-sulfur protein)
(matrix)
(intermembrane space)
![Page 17: 10 Oxidative Phosphorylation 2014-2015](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4f31a28ab9b02a36b5f/html5/thumbnails/17.jpg)
Cytochromes - Protein coenzymes - Heme as a tightly bound co-factor - Heme is a tetrapyrrole coordinating a single
atom of Fe(II/III) - Single electron-carrier (Fe2+ Fe3+ + e-)
Cytochrome a - Contains heme A - Membrane-bound Cytochrome b
- Contains heme B - Membrane-bound
Cytochrome c - Contains heme C - Membrane-bound or
diffusible
![Page 18: 10 Oxidative Phosphorylation 2014-2015](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4f31a28ab9b02a36b5f/html5/thumbnails/18.jpg)
The Q cycle in Complex III
![Page 19: 10 Oxidative Phosphorylation 2014-2015](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4f31a28ab9b02a36b5f/html5/thumbnails/19.jpg)
• Electron carriers: 2 Cu ions and 2 heme A groups (cytochrome a proteins)
• Transfers electrons from cytochrome c to oxygen
• 4 cytochrome c (reduced) + 8H+ in + O2
4 cytochrome c (oxidized) + 4H+ out + 2 H2O
• The redox centers only transfer electron one at a time
• Incompletely reduced intermediates (e.g. hydrogen peroxide and hydroxyl free radicals) remain tightly bound until complete reduction to water.
Cytochrome oxidase (Complex IV)
(x2)
(matrix)
(intermembrane space)
![Page 20: 10 Oxidative Phosphorylation 2014-2015](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4f31a28ab9b02a36b5f/html5/thumbnails/20.jpg)
Electron transport and proton pumps
inner membrane
![Page 21: 10 Oxidative Phosphorylation 2014-2015](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4f31a28ab9b02a36b5f/html5/thumbnails/21.jpg)
• A protein gradient is then established across the inner membrane
• The energy stored in the gradient, proton-motive force, has two components: chemical potential energy and electrical potential energy
• The electrochemical energy released when protons flow spontaneously down the gradient can be used to drive the synthesis of ATP from ADP and Pi
Proton gradient
(matrix) (intermembrane space)
![Page 22: 10 Oxidative Phosphorylation 2014-2015](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4f31a28ab9b02a36b5f/html5/thumbnails/22.jpg)
ATP synthesis by ATP synthase • ATP synthase: F0F1 complex in the inner membrane
• Protons flow through the F0 unit down the gradient
• ATP is synthesized by the F1 unit (ATPase) from ADP and Pi
• For every 2 electrons donated by NADH, 2.5 ATPs are synthesized.
• For every 2 electrons donated by FADH2, 1.5 ATPs are synthesized.
NADH + H+ NAD+
![Page 23: 10 Oxidative Phosphorylation 2014-2015](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4f31a28ab9b02a36b5f/html5/thumbnails/23.jpg)
(1) Glycerol 3-P shuttle - Skeletal muscle and brain
(DHAP)
Shuttle systems for NADH generated in cytoplasm
• Inner mitochondrial membrane is impermeable to NADH
• Cytosolic NADH is shuttled indirectly into the mitochondria as reducing equivalents
• Reducing equivalents are molecules that can be transported into the mitochondria
Complex III
Complex IV
![Page 24: 10 Oxidative Phosphorylation 2014-2015](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4f31a28ab9b02a36b5f/html5/thumbnails/24.jpg)
(2) Malate-aspartate shuttle - Liver, kidney, and heart
(Complexes I, III, IV)
![Page 25: 10 Oxidative Phosphorylation 2014-2015](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4f31a28ab9b02a36b5f/html5/thumbnails/25.jpg)
Net profit of aerobic metabolism
If we start from glucose:
- Glycolysis to 2 pyruvate yields: 2 ATP 2 NADH
- Conversion of 2 pyruvate to 2 acetyl-CoA: 2NADH
- Oxidation of 2 acetyl-CoA in the TCA cycle: 20 ATP
Net yield = __________ ATP for complete oxidation of glucose to CO2
Cytosol
2 X 2.5 (malate-aspartate shuttle) = 5 ATP or 2 X 1.5 (glycerol 3-P shuttle) = 3 ATP
Mitochondria = 2 X 2.5 = 5 ATP
32 or 30