1 / 25

Chapter 14 (part 2)

Chapter 14 (part 2). Oxidative phosphorylation. Proton Motive Force ( D p ). PMF is the energy of the proton concentration gradient The chemical ( D pH= pH in – pH out ) potential and the electrical potential( DY= Y in – Y out ) contribute to PMF D G = nf DY and D G = –2.303nRT D pH

callum-holman
Télécharger la présentation

Chapter 14 (part 2)

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 2) Oxidative phosphorylation

  2. Proton Motive Force (Dp) • PMF is the energy of the proton concentration gradient • The chemical (DpH= pHin – pHout) potential and the electrical potential(DY= Yin– Yout) contribute to PMF • DG = nfDY and DG = –2.303nRT DpH • DG for transporting 1 H+ from inner membrane space to matrix = DG = nfDY –2.303nRTDpH • Dp = Dp = DG/nF • Dp = Dy –(0.059)DpH

  3. Proton Motive Force (Dp) • What contributes more to PMF, DY or DpH? • In liver DY=-0.17V and DpH=0.5 • Dp = Dy –(0.059)DpH = -0.17-(0.059)(0.5V) • Dp = -0.20 V • DY/Dp=(-0.17V/-0.20V) X 100% = 85% • 85% of the free energy is derived form DY

  4. Proton Motive Force (Dp) • How much free energy generated from one proton? • DG = nFDP = (1)(96.48kJ/Vmole)(-0.2V) = -19 kJ/mole • To make 1 ATP need 30 kJ/mole. • Need to translocate more than one proton to make one ATP • ETC translocates 10 protons per NADH

  5. ATP Synthase • Proton diffusion through the protein drivesATP synthesis! • Two parts: F1 and F0

  6. Racker & Stoeckenius confirmed Mitchell’s hypothesis using vesicles containing the ATP synthase and bacteriorhodopsin

  7. Binding Change Mechanism • ADP + Pi <-> ATP + H2O • In catalytic site Keq = 1 • ATP formation is easy step • But once ATP is formed, it binds very tightly to catalytic site (binding constant = 10-12M) • Proton induced conformation change weakens affinity of active site for ATP (binding constant = 10-5)

  8. Binding Change Mechanism • Different conformation at 3 catalytic sites • Conformation changes due to proton influx • ADP + Pi bind to open-site in exchange for ATP • Proton driven conformational change (loose site) causes substrates to bind more tightly • ATP is formed in tight-site. • Requires influx of three protons to get one ATP

  9. ATPase is a Rotating Motor • Bound a,b,g subunits to glass slide • Attached a fluroescent actin chain to g subunit. • Hydrolysis of ATP to ADP + Pi cause filament to rotate 120o per ATP.

  10. How does proton flow cause rotation?

  11. Active Transport of ATP, ADP and Pi Across Mitochondrial Inner Membrane • ATP is synthesized in the matrix • Need to export for use in other cell compartments • ADP and Pi must be imported into the matrix from the cytosol so more ATP can be made. • Require the use of transporters

  12. Transport of ATP, ADP and Pi • Adenine nucleotide translocator = ADP/ATP antiport. • Exchange of ATP for ADP causes a change in DY due to net export of –1 charge • Some of the energy generated from the proton gradient (PMF) is used here • Pi is imported into the matrix with a proton using a symport. • Because negative charge on the phosphate is canceled by positive charge on proton no effect on DY, but effects DpH and therefore PMF.

  13. Transport of ATP, ADP and Pi • NRG required to export 1 ATP and import 1 ADP and 1 Pi = NRG generated from influx of one proton. • Influx of three protons required by ATPase to form 1 ATP molecule. • Need the influx of a total of 4 protons for each ATP made.

  14. P/O Ratio • The ratio of ATPs formed per oxygens reduced • e- transport chain yields 10 H+ pumped out per electron pair from NADH to oxygen • 4 H+ flow back into matrix per ATP to cytosol • 10/4 = 2.5 for electrons entering as NADH • For electrons entering as succinate (FADH2), about 6 H+ pumped per electron pair to oxygen • 6/4 = 1.5 for electrons entering as succinate

  15. Regulation of Oxidative Phosphorylation • ADP is required for respiration (oxygen consumption through ETC) to occur. • At low ADP levels oxidative phosphorylation low. • ADP levels reflect rate of ATP consumption and energy state of the cell. • Intramolecular ATP/ADP ratios also impt. • At high ATP/ADP, ATP acts as an allosteric inhibitor for Complex IV (cytochrome oxidase) • Inhibition is reversed by increasing ADP levels.

  16. 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

  17. Physiological Uncoupling • Uncoupling of ETC and Ox-phos occurs in animals as a means to produce heat = nonshivering thermogenesis. • Impt. In hibernating mammals, neborn animals and mammals adapted to cold • Occurs in brown adipose tissues (rich in mitochondria) • Uncoupling protein (UCP) = channel to allow influx of protons to matrix (dissipates proton gradient)

  18. Uncoupling in Plants • Plants generate heat during fruit ripening and to emit odors to attach pollinators. • Plants can by pass normal ATP generating ETC • Alternative ETC in plants does not pump protons, just transfers electron. • All plant have this pathway, actual physiological reason not known

More Related