1 / 23

Chapter 14 (Part 1)

Chapter 14 (Part 1). Electron transport. Chemiosmotic Theory. Electron Transport: Electrons carried by reduced coenzymes are passed through a chain of proteins and coenzymes to drive the generation of a proton gradient across the inner mitochondrial membrane

irisa
Download Presentation

Chapter 14 (Part 1)

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 14 (Part 1) Electron transport

  2. Chemiosmotic Theory • Electron Transport: Electrons carried by reduced coenzymes are passed through a chain of proteins and coenzymes to drive the generation of a proton gradient across the inner mitochondrial membrane • Oxidative Phosphorylation: The proton gradient runs downhill to drive the synthesis of ATP • Electron transport is coupled with oxidative phosphorylation • It all happens in or at the inner mitochondrial membrane

  3. Outer Membrane – Freely permeable to small molecules and ions. Contains porins with 10,000 dalton limit Inner membrane – Protein rich (4:1 protein:lipid). Impermeable. Contains ETR, ATP synthase, transporters. Cristae – Highly folded inner membrane structure. Increase surface area. Matrix- “cytosol” of the mitochondria. Protein rich (500 mg/ml) Contains TCA cycle enzymes, pyruvate dehydrogenase, fatty and amino acid oxidation pathway, DNA, ribosomes Intermembrane Space – composition similar to cytosol

  4. Reduction Potentials • High Eo' indicates a strong tendency to be reduced • Crucial equation: Go' = -nF Eo' • Eo' = Eo'(acceptor) - Eo'(donor) • NADH + ½ O2 + H+  NAD++ H+ + H2O • NAD++ H+ + 2e- NADH Eo’ = -0.32 • ½ O2 + 2e- + 2H+  H2O Eo’ = 0.816 • Go‘= -nF(Eo'(O2) - Eo'(NADH)) • Go‘= -nF(0.82 –(-0.32)) = -nF(1.14) • = -2(96.5 kJ mol-1V-1)(1.136) = -220 kJ mol-1

  5. Electron Transport • Four protein complexes in the inner mitochondrial membrane • A lipid soluble coenzyme (UQ, CoQ) and a water soluble protein (cyt c) shuttle between protein complexes • Electrons generally fall in energy through the chain - from complexes I and II to complex IV

  6. Standard reduction potentials of the major respiratory electron carriers.

  7. NADH + H+ CoQ NAD+ CoQH2 Complex I • NADH-CoQ Reductase • Electron transfer from NADH to CoQ • More than 30 protein subunits - mass of 850 kD • 1st step is 2 e- transfer from NADH to FMN • FMNH2 converts 2 e- to 1 e- transfer • Four H+ transported out per 2 e- FMN Fe2+S FMNH2 Fe3+S

  8. Succinate CoQ Fumarate CoQH2 FAD Fe2+S FADH2 Fe3+S Complex II • Succinate-CoQ Reductase • aka succinate dehydrogenase (from TCA cycle!) • four subunits • Two largest subunits contain 2 Fe-S proteins • Other subunits involved in binding succinate dehydrogenase to membrane and passing e- to Ubiquinone • FAD accepts 2 e- and then passes 1 e- at a time to Fe-S protein • No protons pumped from this step

  9. Q-Cycle UQ • Transfer from the 2 e- carrier ubiquinone (QH2) to Complex III must occur 1 e- at a time. • Works by two single electron transfer steps taking advantage of the stable semiquinone intermediate • Also allows for the pumping of 4 protons out of mitochondria at Complex III • Myxothiazol (antifungal agent) inhibits electron transfer from UQH2 and Complex III. UQ.- UQH2

  10. CoQH2 cyt c red CoQ cyt c ox cyt c1ox cyt b ox Fe2+S cyt c1red cyt b red Fe3+S Complex III • CoQ-Cytochrome c Reductase • CoQ passes electrons to cyt c (and pumps H+) in a unique redox cycle known as the Q cycle • Cytochromes, like Fe in Fe-S clusters, are one- electron transfer agents • cyt c is a water-soluble electron carrier • 4 protons pumped out of mitochondria (2 from UQH2)

  11. cyt c red cyt a ox cyt a3red O2 cyt c ox cyt a red cyt a3ox 2 H2O Complex IV • Cytochrome c Oxidase • Electrons from cyt c are used in a four-electron reduction of O2 to produce 2H2O • Oxygen is thus the terminal acceptor of electrons in the electron transport pathway - the end! • Cytochrome c oxidase utilizes 2 hemes (a and a3) and 2 copper sites • Complex IV also transports H+ (2 protons)

  12. Inhibitors of Oxidative Phosphorylation • Rotenone inhibits Complex I - and helps natives of the Amazon rain forest catch fish! • Cyanide, azide and CO inhibit Complex IV, binding tightly to the ferric form (Fe3+) of a3 • Oligomycin and DCCD are ATP synthase inhibitors

  13. Shuttling Electron Carriers into the Mitochondrion • The inner mitochondrial membrane is impermeable to NADH. • Electrons carried by NADH that are created in the cytoplasm (such as in glycolysis) must be shuttled into the mitochondrial matrix before they can enter the ETS

  14. Glycerol phosphate shuttle

  15. malate/aspartate shuttle system

  16. Electron transport is coupled to oxidative phosphorylation

  17. Uncouplers • Uncouplers disrupt the tight coupling between electron transport and oxidative phosphorylation by dissipating the proton gradient • Uncouplers are hydrophobic molecules with a dissociable proton • They shuttle back and forth across the membrane, carrying protons to dissipate the gradient • w/o oxidative-phosphorylation energy lost as heat • Dinitrophenol once used as diet drug, people ran 107oF temperatures

More Related