This document summarizes oxidative phosphorylation (OXPHOS) and the electron transport chain in mitochondria. It states that OXPHOS is essential for generating ATP through the transfer of electrons from donor molecules like NADH to oxygen. It occurs through five protein complexes embedded in the inner mitochondrial membrane: complex I-IV transfer electrons and pump protons out of the matrix, while complex V uses the proton gradient to drive ATP synthesis. The document provides an overview of each complex and how they facilitate electron transfer and proton pumping to create the electrochemical gradient used for ATP production.

1. Department of Biochemistry, NGMC, Chisapani, Nepal
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Rajesh Chaudhary
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http://www.slideshare.net/RajeshChaudhary10
Note / Remember

2. Biomedical importance
Oxidative phosphorylation (OXPHOS) is essential for
generation of high energy intermediate – ATP.
Inhibition of OXPHOS results into fatal consequences –
myopathy, encephalopathy and lactic acidosis.
Drugs and poisons that inhibits OXPHOS: amobarbital,
cyanide, carbon monoxide.
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3. The system in mitochondria that couples respiration to
generation of high energy intermediate, ATP, is termed as
Oxidative Phosphorylation (OXPHOS).
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— Harper’s Biochemistry, 25th. Edition

4. Respiratory chain collects & oxidizes
reducing equivalents
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5. Phases of metabolism
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Phases
metabolism
1. Primary
2. Secondary /
Intermediate
3. Tertiary

6. Electron transfer reaction in
mitochondria
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7. Mitochondria and Oxidative
phosphorylation
 The transfer of electron is done by the set of protein
complexes.
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Outer mitochondrial membrane

8. Mitochondrial matrix
 The mitochondrial matrix enclosed by the inner membrane,
contains the pyruvate dehydrogenase complex and the
enzymes of the citric acid cycle, the fatty acid b-oxidation
pathway, and the pathways of amino acid oxidation – all
the pathways of fuel oxidation except glycolysis, which takes
place in cytosol.
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— Lehninger’s Principle of Biochemistry, 5th. Edition

9. Mitochondria and Oxidative
phosphorylation
 Mitochondria is the site of oxidative phosphorylation.
 Oxidative phosphorylation (OXPHOS): metabolic pathways in
which cells use enzymes to oxidize nutrients thereby releasing
energy which is used to reform ATP.
 Takes place inside mitochondria.
 During OXPHOS, electrons are transferred from donor to acceptor.
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10. Electrons are funneled to universal electron
acceptor
 Oxidative phosphorylation beings with the entry of electrons
into the respiratory chain.
 Most of these electrons arise from the action of
dehydrogenases that collect electrons from catabolic
pathways and funnel them into universal electron
acceptors – nicotinamide nucleotide (NAD+ or NADP+) of
Flavin nucleotides (FMN or FAD).
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11. Malate-Aspartate shuttle
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12. Requirements for ATP generation from
OXPHOS
 1. An electron donor: NADH and/or FAD(2H)
 2. An electron acceptor: O2
 3. Intact inner mitochondrial membrane that is impermeable to
protons.
 4. All components of electron transport chain.
 5. ATP synthase
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Oxidative phosphorylation is regulated by the rate of ATP utilization !

13. 1. Complex I / NADH
dehydrogenase
2. Complex II / Succinate
dehydrogenase
3. Complex III / Cytochrome b-C1
4. Complex IV / Cytochrome C
oxidase
5. Complex V / ATP synthase
Components of Electron Transport
Chain (ETC)
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Components of ETC

14. Major components of ETC
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Complex III
ETC also contains:
1. Coenzyme Q
2. Cytochrome C

15. With the exception of Coenzyme Q
(CoQ) rest are proteins in ETC !
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16. Electron Transport Chain (ETC)
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17. Chemiosmotic model of ATP generation
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18. Components of ETC
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19. Coenzyme Q
 The only component of ETC that is not protein bound.
 Large hydrophobic side chain of 10 isoprenoid units (50
carbons) confers lipid solubility.
 It is also called Ubiquinone.
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20. Adenosine Triphosphate Synthase
(ATP synthase)
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Also known as
F0F1 ATPase
Stalk

21. Binding-change mechanism for ATP
synthesis
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Link for the video down below: https://www.youtube.com/watch?v=3y1dO4nNaKY

22. Electrons pass through series of membrane-
bound carriers
 Usually carrier molecules are integral proteins with prosthetic
group capable of accepting and donating one or two
electrons.
 Types of electron transfer in OXPHOS
1. Direct transfer of electrons, as in the reduction of Fe3+ to Fe2+.
2. Transfer as a hydrogen atom (H+ + e-).
3. Transfer as hydride ion which bears two electrons (:H-).
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23. Summary of flow of electrons and protons
through four complexes of the respiratory
chain
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24. Proposed sites of inhibition
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25. References
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