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Oxidative Phosphorylation Notes

Pharmacology Notes > BIOL10212 Biochemistry Notes

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LECTURE 17/18 - BIOCHEMISTRY - 16-19/04/18Pathway linked to the citric acid cycle
It requires aerobic conditions
Electrons transferred from NADH and FADH to O and ATP is formed 2

2 à Respiratory electron-transport chain (ETC): oxidation energy used to transport protons and to establish a proton gradient
à ATP synthase uses the free energy of the proton gradient to produce ATP


The membrane forms cristae to give a larger surface area.
The following enzymes are present in the matrix:
à Pyruvate dehydrogenase complex
à Enzymes of the citric acid cycle
à Enzymes catalyzing fatty acid oxidation
Enzymes used for the electron transport chain and ATP synthase are membrane proteins found in the inner membrane.

- Electrons from NADH are accepted by NADH-Q
reductase at the start of the electron transport chain
- Electrons also come from succinate by way of FADH2,
these electrons are accepted by succinate dehydrogenase
- Free energy is released at each step as you move from complex 1 to complex 5
- Complex 4 passes the electrons onto the oxygen reducing it to water FIVE OLIGOMERIC COMPLEXES INVOLVED IN OXIDATIVE
When the electron transport chain was first studied, they found that the enzymes catalysing this metabolic pathway were very large molecules, they called them complexes and numbered them in the sequential order in which they participate in the pathway-

Complexes I-IV - electron transport:
à I - NADH-ubiquinonone oxidoreductase
à II - Succinate-ubiquinone oxidoreductase
à III - Ubiquinol-cytochrome c reductase
à IV - Cytochrome c oxidase
Complex V - ATP synthesis:
à V - ATP synthase

UBIQUINONE / COENZYME Q:-Reduced one electron at a time
It is a hydrophobic molecule due to its long chain, it prefers a lipid environment and therefore remains in the membrane
Electrons are incorporated into the ring
It is reduced 1 electron at a time
The intermediate molecule is a free radical (i.e. it has one electron which is not paired)
Semiquinone (the free radical) then captures the second electron (and two protons) and becomes dihydroquinone - CoenxymeQH2


NADH-ubiquinone oxidoreductase (aka NADHdehydrogenase)
Gets electrons from NADH,
passes them on to ubiquinone and makes ubiquinol

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