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Chapter 9 - Part 4

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  • Oxidation refers to the loss of electrons to any electron acceptor, not just to oxygen. Uses exergonic flow of electrons through ETC to pump H+ across membrane.
  • Pumping H+ across membrane … what is energy to fuel that? Can’t be ATP! that would cost you what you want to make! Its like cutting off your leg to buy a new pair of shoes. :-( Flow of electrons powers pumping of H + O 2 is 2 oxygen atoms both looking for electrons
  • Electrons move from molecule to molecule until they combine with O & H ions to form H 2 O It’s like pumping water behind a dam -- if released, it can do work
  • Chemiosmosis is the diffusion of ions across a membrane. More specifically, it relates to the generation of ATP by the movement of hydrogen ions across a membrane. Hydrogen ions (protons) will diffuse from an area of high proton concentration to an area of lower proton concentration. Peter Mitchell proposed that an electrochemical concentration gradient of protons across a membrane could be harnessed to make ATP. He likened this process to osmosis, the diffusion of water across a membrane, which is why it is called chemiosmosis.
  • Where did the glucose come from? from food eaten Where did the O 2 come from? breathed in Where did the CO 2 come from? oxidized carbons cleaved off of the sugars (Krebs Cycle) Where did the CO 2 go? exhaled Where did the H 2 O come from? from O 2 after it accepts electrons in ETC Where did the ATP come from? mostly from ETC What else is produced that is not listed in this equation? NAD, FAD, heat!
  • What if you have a chemical that punches holes in the inner mitochondrial membrane?

Transcript

  • 1. Cellular Respiration Stage 4: Electron Transport Chain
  • 2. Cellular respiration
  • 3. What’s the point? The point is to make ATP ! ATP
  • 4. ATP accounting so far…
    • Glycolysis  2 ATP
    • Kreb’s cycle  2 ATP
    • Life takes a lot of energy to run, need to extract more energy than 4 ATP !
    A working muscle recycles over 10 million ATPs per second There’s got to be a better way! I need a lot more ATP !
  • 5. There is a better way!
    • Electron Transport Chain
      • series of proteins built into inner mitochondrial membrane
        • along cristae
        • transport proteins & enzymes
      • transport of electrons down ETC linked to pumping of H + to create H + gradient
      • yields ~36 ATP from 1 glucose !
      • only in presence of O 2 ( aerobic respiration )
    That sounds more like it ! O 2
  • 6. Mitochondria
    • Double membrane
      • outer membrane
      • inner membrane
        • highly folded cristae
        • enzymes & transport proteins
      • intermembrane space
        • fluid-filled space between membranes
    Oooooh ! Form fits function !
  • 7. Electron Transport Chain Intermembrane space Mitochondrial matrix Q C NADH dehydrogenase cytochrome bc complex cytochrome c oxidase complex Inner mitochondrial membrane
  • 8. Remember the Electron Carriers? G3P Glycolysis Krebs cycle 8 NADH 2 FADH 2 2 NADH Time to break open the piggybank ! glucose
  • 9. Electron Transport Chain intermembrane space mitochondrial matrix inner mitochondrial membrane NAD + Q C NADH H 2 O H + e – 2H + + O 2 H + H + e – FADH 2 NADH dehydrogenase cytochrome bc complex cytochrome c oxidase complex FAD e – H H  e- + H + NADH  NAD + + H H Building proton gradient ! What powers the proton (H + ) pumps?… 1 2 p e
  • 10. Stripping H from Electron Carriers
    • Electron carriers pass electrons & H + to ETC
      • H cleaved off NADH & FADH 2
      • electrons stripped from H atoms  H + ( protons )
        • electrons passed from one electron carrier to next in mitochondrial membrane (ETC)
        • flowing electrons = energy to do work
      • transport proteins in membrane pump H + ( protons ) across inner membrane to intermembrane space
    ATP ADP + P i TA-DA !! Moving electrons do the work ! H + H + H + H + H + H + H + H + H + H + H + H + NAD + Q C NADH H 2 O H + e – 2H + + O 2 H + H + e – FADH 2 1 2 NADH dehydrogenase cytochrome bc complex cytochrome c oxidase complex FAD e –
  • 11. But what “pulls” the electrons down the ETC? electrons flow downhill to O 2 oxidative phosphorylation O 2 H 2 O
  • 12. Electrons flow downhill
    • Electrons move in steps from carrier to carrier downhill to oxygen
      • each carrier more electronegative
      • controlled oxidation
      • controlled release of energy
    make ATP instead of fire !
  • 13. We did it!
    • Set up a H + gradient
    • Allow the protons to flow through ATP synthase
    • Synthesizes ATP
    • ADP + P i  ATP
    ATP Are we there yet? “ proton-motive” force H + ADP + P i H + H + H + H + H + H + H + H +
  • 14.
    • The diffusion of ions across a membrane
      • build up of proton gradient just so H+ could flow through ATP synthase enzyme to build ATP
    Chemiosmosis Chemiosmosis links the Electron Transport Chain to ATP synthesis So that’s the point !
  • 15. Peter Mitchell
    • Proposed chemiosmotic hypothesis
      • revolutionary idea at the time
    1961 | 1978 1920-1992 proton motive force
  • 16. H + H + O 2 + Q C ATP Pyruvate from cytoplasm Electron transport system ATP synthase H 2 O CO 2 Krebs cycle Intermembrane space Inner mitochondrial membrane 1. Electrons are harvested and carried to the transport system. 2. Electrons provide energy to pump protons across the membrane. 3. Oxygen joins with protons to form water . 2H + NADH NADH Acetyl-CoA FADH 2 ATP 4. Protons diffuse back in down their concentration gradient, driving the synthesis of ATP . Mitochondrial matrix 2 1 H + H + O 2 H + e - e - e - e - ATP
  • 17. Cellular respiration 2 ATP 2 ATP ~36 ATP + + ~40 ATP
  • 18. Summary of cellular respiration
    • Where did the glucose come from?
    • Where did the O 2 come from?
    • Where did the CO 2 come from?
    • Where did the CO 2 go?
    • Where did the H 2 O come from?
    • Where did the ATP come from?
    • What else is produced that is not listed in this equation?
    • Why do we breathe?
    C 6 H 12 O 6 6O 2 6CO 2 6H 2 O ~40 ATP  + + +
  • 19. Taking it beyond…
    • What is the final electron acceptor in Electron Transport Chain?
    • ETC backs up
      • nothing to pull electrons down chain
      • NADH & FADH 2 can’t unload H
    • ATP production ceases
    • cells run out of energy
    • and you die !
    O 2
    • So what happens if O 2 unavailable?
    NAD + Q C NADH H 2 O H + e – 2H + + O 2 H + H + e – FADH 2 1 2 NADH dehydrogenase cytochrome bc complex cytochrome c oxidase complex FAD e –
  • 20. What’s the point? The point is to make ATP ! ATP