BC351 Lecture 12 Metabolism Oxidative Phosphorylation Terms Electron transport chain Flavoprotein Coenzyme Q Cytochromes Iron sulfur proteins P 2e ratio ETC ATP synthesis coupling Uncoupler Principles 1 The end of glucose and really any metabolic fuel combustion ATP NADH LN09 GLYCOLYSIS C6H12O6 6O2 10 NADH 2 FADH2 LN11 TCA Pyruvate 6H2O 6CO2 ATP NADH FADH2 G 2840 kJ mol ATP LN12 O P a Use of O2 making H2O 2 REDOX again a The movement of electrons derived from glucose through the ETC b How the energy is stored in an electrochemical gradient 3 ATP synthesis a The molecule and the thermodynamics I Overview a Oxidative phosphorylation pgs 707 709 i The majority of ATP production in the cell is accomplished via this process 1 It is broken down into two phases ii Phase 1 Electron transport chain 1 Definition of the Electron transport chain a LN12 1 2 The process involves the flow of electrons through a chain of membrane bound carriers found on the inner membrane of the mitochondria a This flow of electrons is exergonic allowing it to release a large amount of free energy b This free energy is conserved by pumping protons in a thermodynamically unfavorable direction into the inner membrane space IMS of the mitochondria establishing a transmembrane pH electrochemical gradient i The matrix is referred to as the N side and the IMS is referred to as the P side IMS P SIDE LOW pH I III IV II NADH NAD FADH 2 MATRIX N SIDE HIGH pH FAD O 2 2H H 2O E E iii Phase 2 ATP synthesis 1 Protons flow in a thermodynamically favorable direction through specific transport protein called ATP synthase a The free energy available in the exergonic movement of protons back into the matrix of the mitochondria is enough to drive ATP synthesis and is thus conserved LN12 2 II Electron carriers pgs 709 711 a NADH i Produced in many oxidation reactions 1 Gives or takes two electrons b FADH2 i Also produced in oxidation reactions 1 Usually covalently or irreversible bound to a protein a Definition of a flavoprotein i 2 Take up to 2 1 or 2 at a time c FMN i Flavin mononucleotide ii Also makes flavoproteins iii Also takes up to 2 1 or 2 at a time LN12 3 d Coenzyme Q i Definition of Coenzyme Q 1 ii Lipid soluble Q 1 Found in lipid portion of the inner membrane 2 Binds and releases from Complex I III QH iii Up to two electrons one at time 1 Redox states a Ubiquinone Q no electrons QH 2 b Semiquinone radical QH one electron c Ubiquinol QH2 two electrons e Cytochromes heme i Definition of cytochromes heme 1 ii Several Classes 1 a b and c C B 2 Sub classes a cytochrome bL for example 3 All cytochromes can accept and give only 1 electron at a time LN12 4 A f Iron Copper sulfur proteins i Definition of Iron sulfur proteins 1 ii Iron bound to proteins via Cys or His 1 Simple to complex structure iii Can give and accept only 1 electron at a time III The Electron Transport Chain pgs 712 718 a Complex I NADH ubiquinone oxidoreductase i The reaction 1 Oxidizes NADH and reduces ubiquinone ii The structure 1 850 kDa 2 45 subunits a One flavoprotein FMN b Several Fe S proteins with 8 9 Fe S centers iii The sequence of electron transfer NADH Q QH2 NADH NAD FMNH 2 Fe S1 QH 2 H N Fe S2 FMNH QH H N NAD LN12 5 FMN Fe S9 Q 1 NADH to FMN 2 FMN to Fe S a FMN a two electron carrier that can give one electron at a time is a bridge between NADH a two electron carrier donor and Fe S a one electron acceptor 3 Fe S 8 9 to Q a Ubiquinone is converted to ubiquinol and to do so two protons are picked up from the N side i These protons are NOT considered to have been pumped iv The movement of protons a Protons are translocated from the N side to the Pside b This proton pumping is endergonic and the process can be thought of as primary active diffusion i It is primary active diffusion because the energy required to move the proton is derived from the exergonic transfer of electrons from NADH to Q and not from a pre existing ion gradient b Complex II Succinate dehydrogenase i The reaction 1 Oxidizes succinate and reduces ubiquinone ii The structure 1 TCA enzyme 2 4 subunits a 5 different electron carriers 3 C and D subunits are transmembrane proteins LN12 6 a These two subunits contain a heme b group and the binding site for ubiquinone 4 A and B are found on the N side a They contain the binding site for the substrate succinate as well as FAD A and 3 Fe S B groups iii The sequence of electron transfer SUCCINATE Q QH2 SUCCINATE FUMERATE FADH 2 Fe S1 QH 2 H N FADH Fe S2 QH H N FUMARATE FAD Fe S3 Q 1 Succinate to FAD 2 FADH2 to an Fe S 3 An Fe S cascade to Ubiquinone 4 Heme b prevents electron leakage iv The movement of protons 1 The free energy change in the movement of electrons from succinate to ubiquinone is not large enough to pump protons c Complex III Ubiquinone cytochrome c oxidoreductase i The reaction 1 Oxidizes the ubiquinol produced from complex I and II and reduces the peripheral membrane protein cytochrome c LN12 7 ii The structure 1 250 kDa 2 11 subunits a Functional core 3 subunits i Cytochrome b 1 Two hemes bH and bL ii Rieske Fe S protein iii Cytochrome c1 1 Heme c1 b It operates as a dimer 22 subunits in all iii The sequence of electron transfer the Q cycle 1 Round 1 Q CY CLE ROUND 1 P side Cytochrome C 2H P C Fe S C1 Q QH 2 BL Q QH BH H N N side a QH2 to the Fe S and Cyt bL i A split of electrons ii Two protons released to the IMS P side b One electron is passed from Fe S to Cyt c1 which passes it to Cyt c c The other electron is passed to from QH2 Cyt bL i Cyt bL to bH ii Cyt bH to ubiquinone Q 1 Becomes semiquinone QH LN12 8 2 Round 2 2CYT C OX QH2 Q 2 CYT C RED Q CY CLE ROUND 2 P side Cytochrome C 2H P C Fe S C1 Q QH 2 BL QH 2 BH QH H N N side a QH2 to the Fe S and Cyt bL i A split of electrons ii Two protons released to the IMS P side b One electron is passed from Fe S to Cyt c1 which passes it to Cyt c c The other electron is passed to from QH2 Cyt bL i Cyt bL to bH ii Cyt bH to semiquinone QH 1 Becomes ubiquinol QH2 …