1. Chapter 14 - Electron Transport and Oxidative Phosphorylation
The cheetah, whose capacity for aerobic metabolism makes it one of the fastest animals
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2. Oxidative Phosphorylation in Mitochondria
Oxidative phosphorylation is the process by which NADH and FADH2 are oxidized and ATP is formed
NADH and FADH2 are reduced coenzymes from the oxidation of glucose by glycolysis and the citric acid cycle
The Respiratory Electron-transport Chain (ETC) is a series of enzyme complexes embedded in the inner mitochondrial membrane, which oxidize NADH and QH2. Oxidation energy is used to transport protons across the inner mitochondrial membrane, creating a proton gradient
ATP synthase is an enzyme that uses the proton gradient energy to produce ATP
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3. The Mammalian Cell
The final picture of a cell is a very crowded, ordered, dynamic system. There are many processes taking place at once and each process is interrelated and coordinated.
Look at pathways chart.
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4. Mitochondria are energy centers of a cell
Cytosol
Mitochondria
Cells contain several hundred mitochondria, on average.
Mitochondria have two membranes, an inner membrane and an outer membrane
The inside of mitochondria is called the matrix.
Mitochondria use oxygen to generate energy in the form of ATP
ATP – adenosine triphosphate, the energy currency of life.
Mitochondria contain extra DNA encoded some enzymes necessary for its function. – mitochondrial DNA
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5. Fig 14.6
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6. Fig 14.6 Structure of the mitochondrion
Final stages of aerobic oxidation of biomolecules in eukaryotes occur in the mitochondrion
Site of citric acid cycle and fatty acid oxidation which generate reduced coenzymes
Contains electron transport chain to oxidize reduced coenzymes
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7. Overview of oxidative phosphorylation
Fig 14.5
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8. Electron Flow in Oxidative Phosphorylation
Five oligomeric assemblies of proteins associated with oxidative phosphorylation are found in the inner mitochondrial membrane
Complexes I-IV contain multiple cofactors, and are involved in electron transport
Electrons flow through complexes I-IV
Complexes I, III and IV pump protons across the inner mitochondrial membrane as electrons are transferred
Mobile coenzymes: ubiquinone (Q) and cytochrome c serve as links between electron transport complexes
Complex IV reduces O2 to water
Complex V is ATP synthase, which uses the generated proton gradient across the membrane to make ATP
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9. Table 14.1
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10. Cofactors in Electron Transport
NADH donates electrons two at a time to complex I of the electron transport chain
Flavin coenzymes are then reduced
(Complex I) FMN FMNH2
(Complex II) FAD FADH2
FMNH2 and FADH2 donate one electron at a time to ubiquinone (U or coenzyme Q)
All subsequent steps in electron transport proceed by one electron transfers
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11. Mobile electron carriers
1. Ubiquinone (Q) Q is a lipid soluble molecule that diffuses within the lipid bilayer, accepting electrons from Complex I and Complex II and passing them to Complex III.
2. Cytochrome c Associated with the outer face of the inner mitochondrial membrane. Transports electrons from Complex III to Complex IV.
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12. Iron in metalloenzymes
Iron undergoes reversible oxidation and reduction:
Fe3+ + e- (reduced substrate)
Fe2+ + (oxidized substrate)
Enzyme heme groups and cytochromes contain iron
Nonheme iron exists in iron-sulfur clusters (iron is bound by sulfide ions and S- groups from cysteines)
Iron-sulfur clusters can accept only one e- in a reaction
Iron in metalloenzymes
Iron undergoes reversible oxidation and reduction:
Fe3+ + e- (reduced substrate) 
Fe2+ + (oxidized substrate)
Enzyme heme groups and cytochromes contain iron
Nonheme iron exists in iron-sulfur clusters (iron is bound by sulfide ions and S- groups from cysteines)
Iron-sulfur clusters can accept only one e- in a reaction
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13. Fig 7.3 Iron-sulfur clusters
Iron atoms are complexed with an equal number of sulfide ions (S2-) and with thiolate groups of Cys side chains
Fig 7.3 Iron-sulfur clusters
Iron atoms are complexed with an equal number of sulfide ions (S2-) and with thiolate groups of Cys side chains
Heme consists of a tetrapyrrole Porphyrin ring system complexed with iron
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Fig Heme Fe(II)-protoporphyrin IX

14. Complex I. NADH-ubiquinone oxidoreductase
Transfers two electrons from NADH as a hydride ion (H:-) to flavin mononucleotide (FMN), to iron-sulfur complexes, to ubiquinone (Q), making QH2
About 4 protons (H+) are translocated across the inner mitochondrial membrane per 2 electrons transferred
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Fig 14.11

15. Complex II. Succinate-ubiquinone oxidoreductase
Also known as succinate dehydrogenase complex
Transfers electrons from succinate to flavin adenine dinucleotide (FAD) as a hydride ion (H:-), to an iron-sulfur complex, to ubiquinone (Q), making QH2
Complex II does not pump protons
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Fig 14.12

16. Complex III. Ubiquinol-cytochrome c oxidoreductase
Transfers electrons from QH2 to cytochrome c, mediated by iron-sulfur and other cytochromes
Electron transfer from QH2 is accompanied by the translocation of 4 H+ across the inner mitochondrial membrane
Fig 14.13
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17. Complex IV. Cytochrome c oxidase
Uses four-electrons from the soluble electron carrier cytochrome c to reduce oxygen (O2) to water (H2O)
Uses Iron atoms (hemes of cytochrome a) and copper atoms
Pumps two protons (H+) across the inner mitochondrial membrane per pair of electrons, or four H+ for each O2 reduced
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O2 + 4 e- + 4H H2O

18. Complex V: ATP Synthase
F0F1 ATP Synthase uses the proton gradient energy for the synthesis of ATP
Composed of a “knob-and-stalk” structure
F1 (knob) contains the catalytic subunits
F0 (stalk) has a proton channel which spans the membrane.
Passage of protons through the Fo (stalk) into the mitochondrial matrix is coupled to ATP formation
Estimated passage of 3 protons (H+) per ATP synthesized
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19. Fig 14.17 Knob-and-stalk structure of ATP synthase
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20. Mechanism of ATP Synthase
There are 3 active sites, one in each b subunit
Passage of protons through the Fo channel causes the c-e-g unit to rotate inside the a3b3 hexamer, opening and closing the b-subunits, which make ATP
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21. Fig 14.17 Molecular structure of of ATP synthase Prentice Hall c2002
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22. Fig 14.20 Transport of ATP, ADP and Pi across the inner mitochondrial membrane
Adenine nucleotide translocase: unidirectional exchange of ATP for ADP (antiport)
Symport of Pi and H+ is electroneutral
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23. The P:O Ratio molecules of ADP phosphorylated
atoms of oxygen reduced
Translocation of 3H+ required by ATP synthase for each ATP produced
1 H+ needed for transport of Pi, ADP and ATP
Net: 4 H+ transported for each ATP synthesized
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24. Calculation of the P:O ratio
Complex I III IV
#H+ translocated/2e
Since 4 H+ are required for each ATP synthesized:
For NADH: 10 H+ translocated / O (2e-)
P/O = (10 H+/ 4 H+) = 2.5 ATP/O
For succinate (FADH2) substrate = 6 H+/ O (2e-)
P/O = (6 H+/ 4 H+) = 1.5 ATP/O
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25. Regulation of Oxidative Phosphorylation
Overall rate of oxidative phosphorylation depends upon substrate availability and cellular energy demand
Important substrates: NADH, O2, ADP
In eukaryotes intramitochondrial ratio ATP/ADP is a secondary control mechanism
High ratio inhibits oxidative phosphorylation as ATP binds to a subunit of Complex IV
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