Electron Transport and Oxidative Phosphorylation

1
Electron Transport and Oxidative Phosphorylation

• It all reduces down to water.

2
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 ß-oxidation in matrix
• Glycolysis in cytosol

3
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

4
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

5
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

6
Electron Transport Chain
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Complex 1

• Has NADH binding site
• NADH reductase activity
• NADH -? NAD
• NADH ---gt FMN---gtFeS---gt ubiquinone
• ubiquinone ---gt ubiquinone H2
• 4 H pumped/NADH

8
Electron Transport Chain
9
Complex II

• succinate ---FADubiquinone
• Contains coenzyme Q
• FADH2 binding site
• FAD reductase activity
• FADH2 --? FAD

10
Electron Transport Chain
11
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

12
Electron Transport Chain
13
Complex IV

• reduction of oxygen
• cytochrome oxidase
• cyt aa3 red ---gt oxidized state
• oxygen ---gt 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

15
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

• NADH
• 10 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)

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What about NADH from glycolysis?

• NADH made in cytosol
• Cant 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

• http//courses.cm.utexas.edu/jrobertus/ch339k/over
  heads-3/ch19_glycerol-shuttle.jpg

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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

• http//courses.cm.utexas.edu/emarcotte/ch339k/fall
  2005/Lecture-Ch19-2/Slide14.JPG

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Malate Aspartate Shuttlein cytosol

• In liver and heart
• NADH oxidized while reducing oxaloacetate to
  malate
• Malate 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

Mlate Aspartate Shuttlein cytosol
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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 / NADH5.0 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