Electron transport and Oxidative phosphorylation The final piece of the puzzle Take a deep breath and push on

Major Energy Pathways Glycolysis Oxidative phosphorylation pyruvate 3 NADH Glucose Galactose Fructose Mannose Fatty Acids 1 FADH 2 Lactate Amino Acids O2O2 H2OH2O Anaerobic Aerobic Krebs Cycle Acetyl-CoA

Electron Transport and Oxidative Phosphorylation 1. The absolute heart of aerobic metabolism 2. Three Functional Phases Electron transfer from NADH, FADH 2 to O 2 Energy preserved as a proton gradient Proton gradient energy makes ATP We are making ATP from ADP and P i by tapping the oxidative energy generated in the transfer of electrons to O 2

Anatomy of Mitochondria Mitochondria are composed of a dual membrane system: Outer: Porous to all molecules < 10 kDa Inner: Transporter-dependent transport

Inner Membrane Transport in Mitochondria Densely packed with specific membrane transporters and the electron-transporting complexes

Electron Transport The successive passage of electrons through a series of membrane complexes to Oxygen. NADH FMN CoQCyt b Cyt c 1 Cyt c Cyt a+a 3 O2O2 Complex IComplex IIIComplex IV Strategies p219

Transport Mechanism NADH NAD + FMN FMNH 2 CoQ CoQH 2 Cyt b (Fe 3+ ) Cyt b (Fe 2+ ) Cyt c 1 (Fe 3+ ) Cyt c 1 (Fe 2+ ) Cyt c (Fe 3+ ) Cyt c (Fe 2+ ) Cyt a+a 3 (Fe 3+ ) Cyt a+a 3 (Fe 2+ ) O2O2 H2OH2O A bucket-brigade Reduced Oxidized volts volts

Electron Transport Complexes Membranes bound heme proteins or “cytochromes” Iron-Sulfur proteins..high reducing potential Mobile electron carriers –Coenzyme Q –Cytochrome c

Electron Transport NADH O2O2 Complex I Complex III Complex IV CoQ Cyto C Reductive Energy Oxidative Energy Complex II FADH 2 H2H2 Fe2+ H2OH2O

Iron-Sulfur Centers Coenzyme Q

NADH-CoQ Reductase FMN FeS I CoQ Succinate-CoQ Reductase FAD FeS Cyt b 560 II CoQ-cyto c Reductase Cyt b 562 Cyt b 566 FeS Cyt c 1 III Cyto c IV Cu 2+ Cyt a Cyt a 3 O2O2 Mobile Succinate Fumarate NADH Electron Transport Complexes

Energy Time How does the energy of oxidation translate into free energy?  G o’ = –nF  E o ’ F = Faraday’s constant = 96,500 J/mol x volt n = Number of electrons E o ’ = Standard Reduction Potential at pH 7  E =  E o ’ log [electron acceptor] [electron donor] Nernst Equation for one electron transfer Determines  E under non-standard state conditions Textbook p372

 E =  E o ’ log [electron acceptor] [electron donor] pH = pK a + log [proton acceptor] [proton donor]  E (reduction potential) pH pK a  E o ’ (standard reduction potential) Proton AcceptorElectron acceptor (oxidant)(base) Proton Donor (acid)Electron donor (reductant) Acid/Base Redox

Donors (Reductants) Acceptors (Oxidants) e-e-  E o’ = E o’ acceptor - E o’ donor

Eo’Eo’ NADH + H / 2 O 2 NAD + + H 2 O NAD + + 2e + 2H + NADH + H + –0.32 volts 1/2 O 2 + 2e + 2H + H 2 O volts To Arrive at equation: NADH + H + NAD + +2e + 2H volts 1/2 O 2 + 2e + 2H + H 2 O+0.82 volts NADH + H + + 1/2 O 2 NAD + + H 2 O volts  G o’ = –nF  E o ’  G o’ = –220 kJ/mol Top reduces bottom J/Coulomb Coulomb/mol

Shuttles Problem: Cytosolic NADH cannot penetrate the mitochondria Solution: Pass the electrons to something that can penetrate the mitochondria membrane Two Shuttles Glycerol-PO 4 Malate-aspartate FADH 2 2 ATP per NADH c NADH 3 ATP per NADH c Mammalian muscle and liver Insect brain and flight muscle

CH 2 OH C=O CH 2 OP CH 2 OH HO-C-H CH 2 OP CH 2 OH HO-C-H CH 2 OP CH 2 OH C=O CH 2 OP Cytosol Mitochondria Membrane transporter Glycerol-PO 4 Shuttle DHAP Glycerol-PO 4 Flavoprotein dehydrogenase FADH 2 FAD 2ATP NAD + NADH : : : :

COO HO-C-H CH 2 COO C=O CH 2 COO C=O CH 2 COO HO-C-H CH 2 COO H 3 N-C-H CH 2 COO + H 3 N-C-H CH 2 COO + Glu  -Kg Glu NADH OAA Asp Malate-Aspartate L-malate Malate dehydrogenase Malate dehydrogenase NAD + NADH 3ATP Aminotransferase P457 Mitochondria Cytosol