Electron Transport Chain

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Electron Transport and Oxidative Phosphorylation: 

Electron Transport and Oxidative Phosphorylation It all reduces down to water.

Mitochondria: 

Mitochondria outer membrane relatively permeable inner membrane permeable only to those things with specific transporters Impermeable to NADH and FADH 2 Permeable to pyruvate Compartmentalization Kreb's and β-oxidation in matrix Glycolysis in cytosol

Most energy from Redox: 

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 FADH 2 / glucose

Electron Transport Chain: 

Electron Transport Chain Groups of redox proteins On inner mitochondrial membrane Binding sites for NADH and FADH 2 On matrix side of membrane Electrons transferred to redox proteins NADH reoxidized to NAD + FADH 2 reoxidized to FAD

4 Complexes: 

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 O 2 --  H 2 O

Electron Transport Chain: 

Electron Transport Chain

Complex 1: 

Complex 1 Has NADH binding site NADH reductase activity NADH -  NAD + NADH ---> FMN--->FeS---> ubiquinone ubiquinone ---> ubiquinone H 2 4 H + pumped/NADH

Electron Transport Chain: 

Electron Transport Chain

Complex II: 

Complex II succinate ---FAD—ubiquinone Contains coenzyme Q FADH 2 binding site FAD reductase activity FADH 2 --  FAD

Electron Transport Chain: 

Electron Transport Chain

Complex III: 

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 + / FADH 2

Electron Transport Chain: 

Electron Transport Chain

Complex IV: 

Complex IV reduction of oxygen cytochrome oxidase cyt a+a3 red ---> oxidized state oxygen ---> water 2 H + + 2 e - + ½ O 2 --  2 H 2 O transfers e - one at a time to oxygen Pumps 2H + out Total of 10 H + / NADH Total of 6 H + / FADH 2

Totals: 

Totals Proton gradient created as electrons transferred to oxygen forming water 10 H + / NADH 6 H + / FADH 2

Electron Transport Chain: 

Electron Transport Chain

Generation of ATP: 

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: 

Totals NADH 10 H + X 1 ATP = 2.5 ATP 4 H + FADH 2 6 H + X 1 ATP = 1.5 ATP 4 H +

Total ATP from mitochondrial matrix : 

Total ATP from mitochondrial matrix Pyruvate dehydrogenase NADH ……………………………….2.5 ATP Krebs 3 NADH X 2.5 ATP/NADH ……….7.5 ATP FADH 2 X 1.5 ATP / FADH 2 ……….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?: 

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 http://courses.cm.utexas.edu/jrobertus/ch339k/overheads-3/ch19_glycerol-shuttle.jpg

Glycerol phosphate shuttle: 

Glycerol phosphate shuttle In muscle and brain Each NADH converted to FADH 2 inside mitochondrion FADH 2 enters later in the electron transport chain Produces 1.5 ATP

Total ATP per glucose in muscle and brain : 

Total ATP per glucose in muscle and brain Gycerol phosphate shuttle 2 NADH per glucose -  2 FADH 2 2 FADH 2 X 1.5 ATP / FADH 2 ……….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 Shuttle http://courses.cm.utexas.edu/emarcotte/ch339k/fall2005/Lecture-Ch19-2/Slide14.JPG

Malate – Aspartate Shuttle in cytosol: 

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 – 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 : 

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: 

Summary Total ATP / glucose Muscle and brain 30.0 ATP Uses glycerol phosphate shuttle Heart and liver 32.0 ATP Uses malate aspartate shuttle