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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)
Oxidative phos:
~26-28ATP
TOTAL:
~30-32ATP
Occurs in mitochondria
K, lec18, p2
2FADH2 (3ATP)
Oxidative Phosphorylation
What 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 enzymes
Fatty acid oxidation enzymes (discuss later)
Oxidative Phosphorylation
Summary
F type transporter
ATP synthase
Oxidative Phosphorylation
History
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
K, lec18, p16
DNP-treated mito endlessly consume O2 with NO ATP synthesis
2. Artificial H+ gradients drive ATP synthesis
K, lec18, p17
Oxidative Phosphorylation
What 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 2eFMN can carry 1 or 2e-
Oxidative Phosphorylation
Membrane bound
Hydrophobic quinone (coenzyme Q)
Q can carry 1 or 2eQ floats free in lipid bilayer and ferries 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
FeS carry 1 e-, found in complexes I, II, and III, Fe2+ or Fe3+
Oxidative Phosphorylation
Cytochrome c
Peripheral membrane protein that shuttles e- between complexes
III and IV
Fe is linked to His and Met side chains
K, lec 18, p11
Oxidative Phosphorylation
Electron transport chain (respiratory chain)
Series of oxidation/reduction components that carry electrons
Protein
e- carrying components
Complex I
(NADH-Q dehydrogenase)
FMN, FeS
Complex II
(Succinate-Q dehydrogenase)
FAD, FeS
Coenzyme Q
itself
Complex III
(Cytochrome reductase)
Cyt bH, Cyt bL, FeS, Cyt c1
Cytochrome c
itself
Complex IV
(cytochrome oxidase)
Cyt a, Cyt a3, CuA, CuB
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 oxidoreductase
NADH 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 oxidase
Cytocrome c to molecular O2 (reducing it to H2O)
Oxidative Phosphorylation
ATP synthase
Multiprotein complex
3H+ pass through for each ATP made
K, lec18, p18
OUTER MEMBRANE
Oxidative Phosphorylation
Energetics of Ox. Phos.
1/2 O2 + NADH + H+ ⇔ H2O + NAD+
ΔG˚ = -220 kJ/mol
An electrochemical gradient across the inner membrane is formed:
electrical: outside is more positive
chemical: proton concentration gradient (pHout is 1.4 units < pHin
Energy of 3H+ transported drives ATP synthesis
ADP + Pi + 3H+ ⇔ ATP + H2O
ΔG˚ = +30.5 kJ/mol
Oxidative Phosphorylation
Control
Ox. Phos cannot occur without:
source of e- (NADH)
sink for e- (O2)
substrates for ATP synthase (ADP and Pi)
[ADP] is limiting factor
Oxidative Phosphorylation
How does ATP made in mito get out?