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(Lodish)

lumen. (Lodish). Reduction of NADP+---proton consumption (dog elimination!) on the stromal side 2. Pumping from the stroma to the lumen by cytochrome b6f Plastiquinone- translocation of protons from stroma to lumen

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(Lodish)

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  1. lumen (Lodish)

  2. Reduction of NADP+---proton consumption (dog elimination!) on the stromal side • 2. Pumping from the stroma to the lumen by cytochrome b6f • Plastiquinone- translocation of protons from stroma to lumen • The splitting of water in the lumen—proton production on lumen side (new dogs in the doghouse!) Contributions to the proton gradient Now have ATP and NADPH for Calvin cycle. Figure 6.15 (Cell View):

  3. Light Reactions of Photosynthesis Photophosphorylation produces NADPH and ATP. Why? To give to the Dark Reactions to help make carbohydrates 1. The energy from the sun is used to set up a H+ gradient with high H+ inside thylakoids 2. When H+ flow out (through the CFo/CF1), ATP is made in the stroma The initial e- donor is H2O and the final e- acceptor is NADP+

  4. In both mitochondria and chloroplasts, H+ flux is coupled to ATP synthesis In both, ATP is made when H+ flow from the low pH side to high pH side F1 of mitochondria CF1 of chloroplasts H+ ADP + Pi ATP H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ Low [H+] High pH High [H+] Low pH Membrane

  5. The CF1/CFo can make ATP in vitro All of this is done in the dark Step 1. Put thylakoids in pH =4.0 Which direction is the pmf? pH 7 CF1 faces outside. Lower [H+] inside inward pH 4 Step 2. Wait until pH=4.0 inside. Load up H+ inside. pH = 4 is high [H+] inside pH 4 pH 4 Which direction is the pmf now? Step 3. Move thylakoids to pH=7.0 and add ADP+Pi. High [H+] in, low [H+] out ADP+ Pi ATP outward pH 4 What provides the energy for ATP synthesis? pH 7 The H+ gradient Is e- transport necessary for ATP synthesis in vitro?

  6. How do thylakoid membranes harvest light to make NADPH and ATP? Five different things that can happen to light after it hits a pigment 5. Reflected 4. Passed along to another energy carrier Light Pigment pigment 3. Transmitted Emitted 1. Heat 2. Fluorescence No change in wavelength Emitted at a longer wavelength Why are isolated pigments (like chlorophyll) fluorescent but chloroplasts aren’t?

  7. The “Z-scheme” for electron transport in thylakoids Low Reduction Potential *Excited State P700 Remember: In a redox couple, electrons can only be passed to a compound with a higher (more positive) reduction potential (Eo value). *Excited State P680 P700 is part of PSI High Reduction Potential Ground State P700 Ground State P680 P680 is part of PSII • The excited state of P680 now has a low enough Eo value to pass electrons to PQ and the rest of the electron transport chain but the ground state of P700 is too high to pass e- further • Light energy at PSI is needed to lower the Eo value of P700 so that it can pass electrons to the rest of the e- transport chain and, ultimately, to NADP+ • Light provides energy to split water and lower Eo value of P680 (to P680*)

  8. Summary of Light Reactions • PSII (P680) uses light energy to split water by photolysis: H2O H+ + O2 + e- A. The H+ contribute to the H+ gradient in the lumen B. The electrons are passed to the e- transport chain and provide energy for more H+ pumping 2. Electrons passed to PQ and H+ go to the lumen to increase [H+] in lumen 3. Cytb6/f complex accepts e- (GER) and pumps some more H+ into the lumen 4. Electrons passed to PC and PSI (P700) • Electrons passed to NADP+ to make NADPH • The pmf of the H+ gradient is used to make ATP in the stroma Why do plants need water, light and CO2 to grow?

  9. Some inhibitors of photosynthesis(see p.231) • DCMU. We will use it in our lab to block electron transport from PSII to PQ • Atrazine (herbicide): Blocks e- transport from PSII to PQ. Why doesn’t it kill us? • DCIP: Artificial electron acceptor that “steals” electrons from PQ. We will use this in our labs too. • Paraquat: “Steals” electrons from PSI so that NADP+ doesn’t get reduced to NADPH. It is another herbicide

  10. Chloroplasts H2O oxidized to O2 Energy required (light) Makes sugars from CO2 H+ high inside thylakoids CF1 faces out (into the stroma) H+ efflux during ATP synthesis (into the stroma) Mitochondria O2 reduced to H2O Energy produced (ATP) Makes CO2 from sugars H+ high outside inner membrane F1 faces in (into the matrix) H+ influx during ATP synthesis (into the matrix)

  11. The Circle of Life From another book: “Solar energy is the ultimate source of all biological energy.” SUN Photosynthetic Cells In chloroplasts CO2 H2O O2 Carbohydrates In mitochondria Heterotrophic Cells (us) Chloroplasts use energy from light to make carbohydrates and generate O2 Mitochondria produce water and CO2 from carbohydrates and O2

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