Electron Transport and
Oxidative Phosphorylation
It all reduces down to water.
Mitochondria
• outer membrane relatively permeable
• inner membrane permeable only to those
things with specific transporters
– Impermeable to NADH and FADH2
– Permeable to pyruvate
• Compartmentalization
– Kreb's and β-oxidation in matrix
– Glycolysis in cytosol
Most energy from Redox
• electrons during metabolic reactions sent to
NAD and FAD
– Glycolysis
• In cytosol
• produces 2 NADH
– Pyruvate dehydrogenase reaction
• In mitochondrial matrix
• 2 NADH / glucose
– Krebs
• In mitochondrial matrix
• 6 NADH and 2 FADH2 / glucose
Electron Transport Chain
• Groups of redox proteins
– On inner mitochondrial membrane
– Binding sites for NADH and FADH2
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On matrix side of membrane
Electrons transferred to redox proteins
NADH reoxidized to NAD+
FADH2 reoxidized to FAD
4 Complexes
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proteins in specific order
Transfers 2 electrons in specific order
– Proteins localized in complexes
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•
Embedded in membrane
Ease of electron transfer
– Electrons ultimately reduce oxygen to water
•
2 H+ + 2 e- + ½ O2 -- H2O
Electron Transport Chain
Complex 1
•
Has NADH binding site
– NADH reductase activity
•
NADH - NAD+
– NADH ---> FMN--->FeS---> ubiquinone
– ubiquinone ---> ubiquinone H2
– 4 H+ pumped/NADH
Electron Transport Chain
Complex II
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succinate ---FAD—ubiquinone
– Contains coenzyme Q
– FADH2 binding site
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FAD reductase activity
FADH2 -- FAD
Electron Transport Chain
Complex III
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•
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ubiquinone - ubiquinone ox
while cyt C gets reduced
Also contains cytochromes b
– proton pump 4H+
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Adds to gradient
8 H+ / NADH
4 H+ / FADH2
Electron Transport Chain
Complex IV
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•
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reduction of oxygen
cytochrome oxidase
cyt a+a3 red ---> oxidized state
oxygen ---> water
– 2 H+ + 2 e- + ½ O2 -- 2 H2O
– transfers e- one at a time to oxygen
• Pumps 2H+ out
– Total of 10 H+ / NADH
– Total of 6 H+ / FADH2
Totals
• Proton gradient created as electrons
transferred to oxygen forming water
10 H+ / NADH
6 H+ / FADH2
Electron Transport Chain
Generation of ATP
• Proton dependant ATP synthetase
– Uses proton gradient to make ATP
– Protons pumped through channel on enzyme
• From intermembrane space into matrix
• ~4 H+ / ATP
– Called chemiosmotic theory
Totals
NADH
10 H+ X 1 ATP = 2.5 ATP
4 H+
FADH2
6 H+ X 1 ATP = 1.5 ATP
4 H+
Total ATP from mitochondrial matrix
• Pyruvate dehydrogenase
– NADH ……………………………….2.5 ATP
• Krebs
3 NADH X 2.5 ATP/NADH ……….7.5 ATP
FADH2 X 1.5 ATP / FADH2……….1.5 ATP
GTP X 1 ATP / GTP ……………..1.0 ATP
(from a separate reaction)
Total …………….12.5 ATP
(Per glucose = X 2 = 25 ATP)
What about NADH from glycolysis?
• NADH made in cytosol
• Can’t get into matrix of mitochondrion
• 2 mechanisms
– In muscle and brain
• Glycerol phosphate shuttle
– In liver and heart
• Malate / aspartate shuttle
Glycerol Phosphate shuttle
•
http://courses.cm.utexas.edu/jrobertus/ch339k/overheads-3/ch19_glycerol-shuttle.jpg
Glycerol phosphate shuttle
• In muscle and brain
• Each NADH converted to FADH2 inside
mitochondrion
– FADH2 enters later in the electron transport
chain
– Produces 1.5 ATP
Total ATP per glucose in muscle
and brain
• Gycerol phosphate shuttle
– 2 NADH per glucose - 2 FADH2
– 2 FADH2 X 1.5 ATP / FADH2……….3.0 ATP
– 2 ATP in glycoysis ……………………2.0 ATP
– From pyruvate and Krebs
• 12.5 ATP X 2 per glucose ……………..25.0 ATP
Total = 30.0 ATP/ glucose
Malate – Aspartate Shuttle
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http://courses.cm.utexas.edu/emarcotte/ch339k/fall2005/Lecture-Ch19-2/Slide14.JPG
Malate – Aspartate Shuttle
in cytosol
• In liver and heart
• NADH oxidized while reducing
oxaloacetate to malate
– Malate dehydrogenase
• Malate crosses membrane
Malate – Aspartate Shuttle
in matrix
• Malate reoxidized to oxaloacetate
– Malate dehydrogenase
– NAD+ reduced to NADH
• NADH via electron transport yields 2.5
ATP
Total ATP per glucose in liver and
heart
• Malate – Aspartate Shuttle
– 2 NADH per glucose - 2 NADH
– 2 NADH X 2.5 ATP / NADH…………5.0 ATP
– 2 ATP from glycolysis………………..2.0 ATP
– From pyruvate and Krebs
• 12.5 ATP X 2 per glucose ……………..25.0 ATP
Total = 32.0 ATP/ glucose
Summary
• Total ATP / glucose
– Muscle and brain
30.0 ATP
• Uses glycerol phosphate shuttle
– Heart and liver
• Uses malate aspartate shuttle
32.0 ATP