Lecture 18 Chapters 20 The Electron Transport Chain In all things in nature there is something of the marvelous Aristotle 384 322 B C Wall Piece IV 1985 a kinetic sculpture by George Rhoads 1 Essential Question How do cells oxidize NADH and FADH2 and convert their reducing potential into the chemical energy of ATP 2 Outline Oxidation Reduction reactions Definition of standard reduction potential Organization of the ETC is according to increasing values The components of the mitochondrial ETC The path of e flow and concomitant H transfer in the ETC ROS 3 Overview of the process of complete oxidation of glucose under aerobic conditions Glycolyis TCA Cycle Oxidative Phosphorylation Cellular Respiration generation of Hightransfer potential electron by TCA their flow through respiratory chain and synthesis of ATP 4 Mitochondrial functions are localized in specific compartments eukaryotes Results from Endosymbiotic events most likely from Rickettsia prowazekii pyruvate 5 Cellular Respiration Protonmotive force II I IV III 6 Reduction of NAD http classes midlandstech edu carterp courses bio225 chap05 lecture3 htm 7 The reduction potential E0 or redox potential is a measure of a molecule s tendency to donate or accept electrons A is getting reduced A is an Oxidizing Agent OA A strong oxidizing agent readily accepts electrons and has a positive redox potential E0 Reduction Gain of e Aox Bred Ared Box Oxidation Loss of eB is getting oxidized B is a Reducing Agent RA A strong reducing agent readily donates electrons and has a 8 negative redox potential E0 Measuring Redox Potential electromotive force oxidized 1 M Fumarate Voltmeter 1 M Succinate reduced Together the oxidized and the reduced forms of the substance are referred to as a redox couple 9 o Standard Reduction Potential values can be used to predict the direction of redox reactions pH 7 0 1 1 Fe 3 Cu 2 Fe 2 Cu 0 77 0 16 The o std state reduction potential refers to the partial reactions written as Oxidant e Reductant 10 An Electrochemical Cell E cell Ered Eox 0 16 VV E 0 16 E E 0 77 V 1 Cu Fe3 Cu2 Fe2 red ox ox red E cell 0 16 0 77 An Electrochemical Cell E cell Ered Eox E 0 77 V Fe2 e Fe3 Cu2 e Cu E 0 16 V 2 Cu2 Fe2 Cu Fe3 E cell 0 16 0 77 ox red red ox 12 Predict the direction of redox reactions Consider the oxidation of NADH during Oxidative Phosphorylation NADH H O2 NAD H2O red ox ox red This involves the following two half reactions 1 NAD 2e 2H NADH H 2 O2 2H 2e H2O 0 32 V from table 0 816 V from table Since we are looking for oxidation of NADH reverse reaction 1 so that it is written as oxidation Note 2 1 3 NADH H NAD 2H 2e 0 32 V Now add reactions 2 and 3 to get the overall reaction as written above NADH H O2 NAD H2O whole reaction 2 3 0 816 0 32 V 1 136 V 13 Relation between Std Reduction Potential and G Std State Free Energy of a redox reaction G nF G n F is the standard state free energy change of the whole reaction is the standard state reduction potential diference between the two half cells is the number of e transferred is Faraday s constant F 96500 Coulomb mol or 96500 JV 1mol 1 since 1C 1 JV 1 96 5 kJV 1mol 1 Should be able to calculate G from self calculated given of a whole redox reaction 14 Std Reduction Potential values can be used to predict the direction of redox reactions Consider the oxidation of NADH during Oxidative Phosphorylation NADH H O2 NAD H2O red ox ox red whole reaction 1 136 V G nF 2 96 5 kJV 1mol 1 1 136 V 219 3 kJ mol large ve value Reaction very spontaneous 15 The Electron Transport Chain 4 Cyt c 2 X 4 also to QH2 pool Does NOT go through II Correction Cyt c Is soluble in the intermembrane space NOT the matrix 16 Electrons flow down an energy gradient 0 82 17 Complex I NADH Q reductase complex matrix FMN oxidized flavin mononucleotide 18 Iron sulfur clusters 2Fe 2S cluster 4Fe 4S cluster 19 Complex I NADH Q reductase complex matrix FMN oxidized flavin mononucleotide 20 Coenzyme Q is derived from isoprene 21 Coenzyme Q Ubiquinone UQ Q10 It is a mobile e carrier It is highly hydrophobic and freely difuses in the hydrophobic core of the inner mitochondrial membrane 22 CoQ can exist in one of three oxidation states e 2H e 2e2e 2H 2H e H UQ UQH2 23 Complex II Succinate Q Reductase complex Succinate Q Fumarate QH2 Succinate dehydrogenase 24 Complex III Q Cytochrome C Oxidoreductase cytochrome C Cyt C Q pool Q QH2 Q pool Q QH2 Ubiquinone Q matrix 25 Complex III Q Cytochrome C Oxidoreductase cytochrome C Cyt C Q pool Q QH2 Q pool Q QH2 Ubiquinone Q matrix 26 Complex III Q Cytochrome C Oxidoreductase Q pool Q QH2 Q pool Q QH2 Q pool Q QH2 matrix 27 Cytochrome c Structure Iron Heme A 550 nm 28 Complex IV Cytochrome c Oxidase Overview 29 Complex IV Mechanism Part 1 2 Reduced Cytochrome c 1 2 matrix 3 30 Complex IV Mechanism Part 2 2 Reduced Cytochrome c 5 matrix 4 matrix 31 Complex IV Cytochrome c Oxidase Summary matrix G 231 8 kJ mol 1 Pumped out 32 Oxidative Phosphorylation 4x 4x 2x 33 The Dangerous side to Cellular Respiration Free Radicals A k a Reactive Oxygen Species ROS 2 4 of oxygen molecules consumed by mitochondria are converted into superoxide ions 34 Bad side of ROS Lipid peroxidation membrane damage Polyunsaturated fat only DNA damage 10 000 oxidative hits day Protein oxidation ROS damaged proteins and lipids become reactive radical species themselves and help spread the damage 35 ROS plays a role in development of many diseases Heart s disease Cancer Alzheimer s disease Autoimmune diseases lupus rheumatoid arthritis diabetes Adult respiratory distress syndrome Acute renal failure Cerebrovascular injury Alcoholic liver disease Parkinson s disease Aging 36 Three types of Superoxide Dismutase SOD SOD 1 copper zinc dependent in cytosol SOD 2 Manganese dependent in mitochondria SOD 3 Extracellular copper zinc dependent 37 Superoxide Dismutase SOD 2O2 2H O2 Step 1 O2 Mox Mred O2 Step 2 H2O2 O2 Mred H2O2 Mox 2H SOD 1 is Deficient in 20 of amyotrophic lateral sclerosis ALS 38 Two enzymes convert Hydrogen Peroxide to H2O 2 H2O2 O2 2 H2O Catalase In peroxisomes 39 Blame it on Catalase Gray hair cure Scientists find root cause of discoloration 25 Apr 2013 10 24am EDT By Marc Lallanilla LiveScience 40 Two enzymes convert Hydrogen Peroxide to H2O 2 H2O2 O2 2 H2O Catalase In peroxisomes O22O2 2 GSH2 H2H O2 2 H GS SG 2O 2 H2O Glutathione peroxidase In cytoplasm 41 GSH Reduced form GS SG Disulfide oxidized form 42 The Glutathione Oxidation Reduction Redox Cycle Glutathione reductase Glutathione peroxidase
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