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Oxidative Phosphorylation
What is it?
Process in which ATP is formed as a result of the transfer of electrons from NADH or FADH2 to O2 via a series of electron carriers
Oxidation of glucose:Glycolysis: 2ATP 2NADH (5ATP)
Pyruvate dehyd: 2NADH (5ATP)
Citric acid cycle: 2ATP 6NADH (15ATP) 2FADH2 (3ATP)
Oxidative phos: ~26-28ATP
TOTAL: ~30-32ATP
K, lec18, p2
Occurs in mitochondria
Oxidative PhosphorylationWhat is mitochondria?2 membranes:Inner - only permeable to O2, H2O transporters req’d for ATP, Pi, pyruvate, etc. folding increases surface area (site of ox. phos. machinery)Matrix contains:citric acid cycle enzymesFatty acid oxidation enzymes (discuss later)
Oxidative PhosphorylationSummary
F type transporterATP synthase
Oxidative PhosphorylationHistory
1961 - Peter Mitchell proposed chemiosmotic hypothesis: energy from e- transport is stored in a proton gradient which is then used to make ATP
Experimental support:1. Uncouplers: dinitrophenol carries H+ across membrane, dissipating the H+ gradient
DNP-treated mito endlessly consume O2 with NO ATP synthesis
2. Artificial H+ gradients drive ATP synthesis
K, lec18, p16
K, lec18, p17
Oxidative PhosphorylationWhat are the electron carriers?
NADH, NADPH (cannot cross inner mito membrane, shuttle their e-)FMN, FAD (directly involved in Ox phos)
NADH, NADPH and FADH2 each carry 2e-
FMN can carry 1 or 2e-
Membrane boundHydrophobic quinone (coenzyme Q)Q can carry 1 or 2e- Q floats free in lipid bilayer and moves e- from complexes I and II to III
Oxidative Phosphorylation
Iron-containing proteins (cytochromes and Fe-S proteins)Cyt carry 1 e-, heme, found in complexes III and IV and cytochrome c
Oxidative Phosphorylation
FeS carry 1 e-, found in complexes I, II, and III, Fe2+ or Fe3+
Cytochrome cPeripheral membrane protein that shuttles e- between complexes III and IVFe is linked to His and Met side chains
Oxidative Phosphorylation
K, lec 18, p11
Oxidative Phosphorylation
Electron transport chain (respiratory chain)Series of oxidation/reduction components that carry electrons
Complex I(NADH-Q dehydrogenase)
Complex II(Succinate-Q dehydrogenase)
Coenzyme Q
Complex III(Cytochrome reductase)
Cytochrome c
Complex IV(cytochrome oxidase)
FMN, FeS
FAD, FeS
itself
Cyt bH, Cyt bL, FeS, Cyt c1
itself
Cyt a, Cyt a3, CuA, CuB
Protein e- carrying components
Oxidative Phosphorylation
Order of electron carriers determined by respiratory inhibitors
NADH FMN FeS Q cyt b FeS cyt c1 cyt c cyt a cyt a3 O2
rotenone antimycin A cyanide, azide
Oxidative Phosphorylation
Complex I: NADH:Ubiquinone oxidoreductaseNADH to Q
(Proton pump)
Oxidative Phosphorylation
Complex II: Succinate dehydrogenase Succinate to Q
QH2
Oxidative Phosphorylation
Complex III: Cytochrome bc1 complex or ubiquinone:cytochrome c oxidoreductase Ubiquinol (QH2) to cytocrome c
Oxidative Phosphorylation
Complex IV: Cytochrome oxidaseCytocrome c to molecular O2 (reducing it to H2O)
Oxidative Phosphorylation
ATP synthaseMultiprotein complex3H+ pass through for each ATP made
K, lec18, p18
OUTER MEMBRANE
INNER MEMBRANE
Oxidative PhosphorylationEnergetics of Ox. Phos.
1/2 O2 + NADH + H+ H2O + NAD+
G˚ = -220 kJ/mol
An electrochemical gradient across the inner membrane is formed:electrical: outside is more positivechemical: proton concentration gradient (pHout is 1.4 units < pHin
Energy of 3H+ transported drives ATP synthesis
ADP + Pi + 3H+ ATP + H2OG˚ = +30.5 kJ/mol
Oxidative Phosphorylation
ControlOx. Phos cannot occur without:
source of e- (NADH)sink for e- (O2)substrates for ATP synthase (ADP and Pi)
[ADP] is limiting factor
Inhibit electron transfer
Oxidative Phosphorylation
How does ATP made in mito get out?