Electron Transport Chain

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


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

• On matrix side of membrane• Electrons transferred to redox proteins• NADH reoxidized to NAD+

• FADH2 reoxidized to FAD


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


Complex 1

• Has NADH binding site– NADH reductase activity

• NADH - NAD+

– NADH ---> FMN--->FeS---> ubiquinone

– ubiquinone ---> ubiquinone H2

– 4 H+ pumped/NADH


Complex II

• succinate ---FAD—ubiquinone– Contains coenzyme Q

– FADH2 binding site• FAD reductase activity

• FADH2 -- FAD


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


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


Totals

• Proton gradient created as electrons transferred to oxygen forming water– 10 H+ / NADH

– 6 H+ / FADH2


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

NADH10 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)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


Glycerol Phosphate shuttle


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


Malate – Aspartate Shuttlein cytosol

• In liver and heart

• NADH oxidized while reducing oxaloacetate to malate– Malated dehydrogenase

• Malate crosses membrane


Malate – Aspartate Shuttlein 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 32.0 ATP• Uses malate aspartate shuttle


Electron Transport Chain

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