Electron transport and Oxidative phosphorylation

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

Major Energy Pathways Glucose Glycolysis Fatty Acids Acetyl-CoA Krebs Cycle 1 FADH2 3 NADH O2 H2O Galactose Fructose Mannose Anaerobic Lactate pyruvate Amino Acids Aerobic Oxidative phosphorylation

Electron Transport and Oxidative Phosphorylation 1. The absolute heart of aerobic metabolism 2. Three Functional Phases Electron transfer from NADH, FADH2 to O2 Energy preserved as a proton gradient Proton gradient energy makes ATP We are making ATP from ADP and Pi by tapping the oxidative energy generated in the transfer of electrons to O2

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

Strategies p219 Electron Transport The successive passage of electrons through a series of membrane complexes to Oxygen. Cyt c1 Cyt a+a3 O2 CoQ Cyt b Cyt c NADH FMN Complex I Complex III Complex IV

Transport Mechanism .. .. .. .. .. .. .. .. Cyt a+a3 (Fe2+) Cyt b (Fe3+) Cyt c1 (Fe2+) Cyt c (Fe3+) FMN CoQH2 O2 NAD+ Cyt b (Fe2+) Cyt c1 (Fe3+) Cyt c (Fe2+) Cyt a+a3 (Fe3+) H2O FMNH2 CoQ Reduced Oxidized A bucket-brigade NADH + 0.82 volts -0.32 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 -0.32 Reductive Energy Complex I CoQ H2 Complex II Complex III Cyto C Fe2+ FADH2 O2 Complex IV H2O +0.82 Oxidative Energy

Iron-Sulfur Centers Coenzyme Q

Mobile III I IV CoQ-cyto c Reductase Cu2+ Cyt a Cyt a3 NADH-CoQ Reductase Cyt b562 Cyt b566 FeS Cyt c1 FMN FeS II Succinate-CoQ Reductase FAD FeS Cyt b560 Succinate Fumarate NADH CoQ O2 Cyto c Electron Transport Complexes

[electron acceptor] E = Eo’ + 0.06 log [electron donor] Energy Time Textbook p372 How does the energy of oxidation translate into free energy? DGo’ = –nFDEo’ F = Faraday’s constant = 96,500 J/mol x volt n = Number of electrons Eo’ = Standard Reduction Potential at pH 7 Nernst Equation for one electron transfer Determines E under non-standard state conditions

[proton acceptor] pH = pKa + log [proton donor] Redox Acid/Base [electron acceptor] E = Eo’ + 0.06 log [electron donor] E (reduction potential) pH pKa Eo’ (standard reduction potential) Proton Acceptor (base) Electron acceptor (oxidant) Proton Donor (acid) Electron donor (reductant)

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

NAD+ + H2O NADH + H+ + 1/2 O2 Eo’ NAD+ + 2e + 2H+ NADH + H+ 1/2 O2 + 2e + 2H+ H2O Top reduces bottom NADH + H+ NAD+ +2e + 2H+ 1/2 O2 + 2e + 2H+ H2O NADH + H+ + 1/2 O2 NAD+ + H2O Coulomb/mol –0.32 volts +0.82 volts To Arrive at equation: +0.32 volts +0.82 volts +1.14 volts J/Coulomb DGo’ = –nFDEo’ DGo’ = –220 kJ/mol

Insect brain and flight muscle Mammalian muscle and liver Shuttles Problem: Cytosolic NADH cannot penetrate the mitochondria Solution: Pass the electrons to something that can penetrate the mitochondria membrane Two Shuttles Glycerol-PO4 FADH2 2 ATP per NADHc Malate-aspartate 3 ATP per NADHc NADH

Glycerol-PO4 Shuttle CH2OH CH2OH HO-C-H HO-C-H CH2OP CH2OP CH2OH CH2OH Membrane transporter C=O C=O CH2OP CH2OP FAD FADH2 Cytosol : NADH NAD+ : Glycerol-PO4 DHAP Flavoprotein dehydrogenase Mitochondria : : 2ATP

COO COO NAD+ HO-C-H HO-C-H COO COO CH2 CH2 C=O C=O COO COO Glu a-Kg CH2 CH2 COO COO a-Kg COO COO Glu + + H3N-C-H H3N-C-H CH2 CH2 NADH NAD+ COO COO Malate-Aspartate P457 NADH Aminotransferase Malate dehydrogenase OAA L-malate Cytosol Mitochondria Malate dehydrogenase Aminotransferase 3ATP Asp

Electron transport and Oxidative phosphorylation