It all reduces down to water. The Electron Transport Chain and Oxidative Phosphorylation Prof. S. Kajuna 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 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

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 succinate ---FAD—ubiquinone Contains coenzyme Q FADH2 binding site FAD reductase activity FADH2 -- FAD

Electron Transport Chain

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

Electron Transport Chain

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

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

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 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 Mlate – Aspartate Shuttle in cytosol

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