Electron Transport and Oxidative Phosphorylation 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 FADH 2 –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 FADH 2 / glucose

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 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 e - + ½ O 2 --  H 2 O

Electron Transport Chain

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

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

Electron Transport Chain

Complex IV reduction of oxygen cytochrome oxidase cyt a+a3 red ---> oxidized state oxygen ---> water –2 H 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 Proton gradient created as electrons transferred to oxygen forming water 10 H + / NADH 6 H + / FADH 2

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 + FADH 2 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 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? 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 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 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 …………… ATP Total = 30.0 ATP/ glucose

Malate – Aspartate Shuttle

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 …………… ATP Total = 32.0 ATP/ glucose

Summary Total ATP / glucose –Muscle and brain30.0 ATP Uses glycerol phosphate shuttle –Heart and liver32.0 ATP Uses malate aspartate shuttle