cell metabolism part 1
TRANSCRIPT
Electron Transport and Oxidative Phosphorylation
It all reduces down to water.
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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
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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
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Electron Transport Chain
• Groups of redox proteins– On inner mitochondrial membrane
– Binding sites for NADH and FADH2
• On matrix side of membrane• Electrons transferred to redox proteins• NADH reoxidized to NAD+
• FADH2 reoxidized to FAD
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4 Complexes
• proteins in specific order
• Transfers 2 electrons in specific order– Proteins localized in complexes
• Embedded in membrane• Ease of electron transfer
– Electrons ultimately reduce oxygen to water• 2 H+ + 2 e- + ½ O2 -- H2O
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Electron Transport Chain
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Complex 1
• Has NADH binding site– NADH reductase activity
• NADH - NAD+
– NADH ---> FMN--->FeS---> ubiquinone
– ubiquinone ---> ubiquinone H2
– 4 H+ pumped/NADH
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Electron Transport Chain
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Complex II
• succinate ---FAD—ubiquinone– Contains coenzyme Q
– FADH2 binding site• FAD reductase activity
• FADH2 -- FAD
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Electron Transport Chain
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Complex III
• ubiquinone - ubiquinone ox
• while cyt C gets reduced
• Also contains cytochromes b– proton pump 4H+
• Adds to gradient– 8 H+ / NADH
– 4 H+ / FADH2
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Electron Transport Chain
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Complex IV
• 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
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Totals
• Proton gradient created as electrons transferred to oxygen forming water– 10 H+ / NADH
– 6 H+ / FADH2
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Electron Transport Chain
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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
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Totals
NADH10 H+ X 1 ATP = 2.5 ATP
4 H+
FADH2
6 H+ X 1 ATP = 1.5 ATP
4 H+
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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)www.freelivedoctor.com
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
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Glycerol Phosphate shuttle
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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
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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
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Malate – Aspartate Shuttle
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Malate – Aspartate Shuttlein cytosol
• In liver and heart
• NADH oxidized while reducing oxaloacetate to malate– Malated dehydrogenase
• Malate crosses membrane
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Malate – Aspartate Shuttlein matrix
• Malate reoxidized to oxaloacetate– Malate dehydrogenase– NAD+ reduced to NADH
• NADH via electron transport yields 2.5 ATP
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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
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Summary
• Total ATP / glucose– Muscle and brain 30.0 ATP
• Uses glycerol phosphate shuttle
– Heart and liver 32.0 ATP• Uses malate aspartate shuttle
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