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 kineCc sculpture by George Rhoads 1 EssenCal QuesCon How do cells oxidize NADH and FADH2 and convert their reducing potenCal into the chemical energy of ATP 2 Outline OxidaCon ReducCon reacCons De niCon of standard reducCon potenCal OrganizaCon of the ETC is according to increasing values The components of the mitochondrial ETC The path of e ow and concomitant H transfer in the ETC ROS 3 Overview of the process of complete oxidaCon of glucose under aerobic condiCons Glycolyis TCA Cycle OxidaCve PhosphorylaCon Cellular RespiraCon generaCon of High transfer potenCal electron by TCA their ow through respiratory chain and synthesis of ATP 4 Mitochondrial funcCons are localized in speci c compartments eukaryotes Results from EndosymbioCc events most likely from RickeCsia prowazekii pyruvate 5 Cellular RespiraCon Proton moCve force II I IV III 6 ReducCon of NAD hep classes midlandstech edu carterp courses bio225 chap05 lecture3 htm 7 The reducCon potenCal E0 or redox potenCal is a measure of a molecule s tendency to donate or accept electrons A is geing reduced A is an Oxidizing Agent OA A strong oxidizing agent readily accepts electrons and has a posi ve redox potenCal E0 ReducCon Gain of e Aox Bred Ared Box OxidaCon Loss of e B is geing oxidized B is a Reducing Agent RA A strong reducing agent readily donates electrons and has a 8 nega ve redox potenCal E0 Measuring Redox PotenCal electromoCve 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 ReducCon PotenCal values can be used to predict the direcCon of redox reacCons pH 7 0 Fe 3 Cu 2 Fe 2 Cu 1 0 77 1 0 16 The o std state reducCon potenCal refers to the parCal reacCons wrieen as Oxidant e Reductant 10 An Electrochemical Cell E cell Ered Eox E 0 77 V 1 Cu Fe3 Cu2 Fe2 E cell 0 16 0 77 red ox ox red E 0 16 V 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 direcCon of redox reacCons Consider the oxida on of NADH during Oxida ve Phosphoryla on NADH H O2 NAD H2O red ox ox red This involves the following two half reacCons 1 NAD 2e 2H NADH H 0 32 V from table 2 O2 2H 2e H2O 0 816 V from table Since we are looking for oxidaCon of NADH reverse reacCon 1 so that it is wrieen as oxidaJon Note 2 1 3 NADH H NAD 2H 2e 0 32 V Now add reacCons 2 and 3 to get the overall reacCon as wrieen above NADH H O2 NAD H2O whole reacCon 2 3 0 816 0 32 V 1 136 V 13 RelaCon between Std ReducCon PotenCal and G Std State Free Energy of a redox reacCon G nF G is the standard state free energy change of the whole reacCon is the standard state reducCon potenCal di erence between the two half cells n is the number of e transferred F 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 reacCon 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 ReacCon very spontaneous 15 The Electron Transport Chain 4 Cyt c 2 X 4 also to QH2 pool Does NOT go through II CorrecCon Cyt c Is soluble in the intermembrane space NOT the matrix 16 Electrons ow down an energy gradient 0 82 17 Complex I NADH Q reductase complex matrix FMN oxidized avin mononucleoCde 18 Iron sulfur clusters 2Fe 2S cluster 4Fe 4S cluster 19 Complex I NADH Q reductase complex matrix FMN oxidized avin mononucleoCde 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 di uses in the hydrophobic core of the inner mitochondrial membrane 22 CoQ can exist in one of three oxidaCon states e 2H e 2H 2e2e 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 OxidaCve PhosphorylaCon 4x 4x 2x 33 The Dangerous side to Cellular RespiraCon Free Radicals A k a ReacCve Oxygen Species ROS 2 4 of oxygen molecules consumed by mitochondria are converted into superoxide ions 34 Bad side of ROS Lipid peroxidaCon membrane damage Polyunsaturated fat only DNA damage 10 000 oxidaCve hits day Protein oxidaCon ROS damaged proteins and lipids become reacCve 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 arthriCs 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 H O O O2 2 2 2 O2 Step 1 Mox Mred O2 Step 2 Mred H2O2 Mox 2H SOD 1 is De cient 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 ScienCsts nd root cause of discoloraCon 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 2 H O22 O2 2 GSH 2 H O2 2 H GS SG 2 2O H2O Glutathione peroxidase In cytoplasm 41 GSH Reduced form GS SG Disul de oxidized form 42 The Glutathione OxidaCon ReducCon …
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