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Photosynthesis

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    1342
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    Compare photosynthesis to respiration:   
     
    Respiration
    C6H12O6 + 6O2 → 6CO2 + 6H2O  
    ΔGo’ = -2840 kJ/mol 
     
    Photosynthesis in green plants
    6 CO2 + 6H2O → C6H12O6 + 6O2 
    ΔGo’ = +2840 kJ/mol   (Unfavorable  ΔGo’ explains the need for energy input.) 
     
    Compare photosynthesis in plants with bacteria
     
    Plants (divided by 6, H2O added to each side)
    CO2 + 2 H2O → C(H2O) + O2 + H2O
     
    Photosynthesis in green sulfur bacteria
    CO2 + 2H2S → C(H2O) + 2S + H2O
     
    Photosynthesis in purple non-sulfur bacteria
    CO2 + 2CH3CHOHCH3 → C(H2O) + 2CH3COCH3+ H2O
                  isopropanol   acetone
     
    C O2 + 2 CH3CHOHCOOH → C(H2O) + 2 CH3COHCOOH + H2O
                  lactate   pyruvate
     
    Generalize
    CO2 + 2H2D → C(H2O) + 2D + H2O
    D = H/electron donor
     
    photosyn.png
    So the light reactions must produce NADPH and ATP to provide energy and H
     
     
    The light reactions occur on the thylakoid membranes of chloroplasts (or the plasma membrane or internal membranes of bacteria).
    Picture 4.png
     
    (Note the “lumen” of thylakoids)
     
    The light reactions occur on the thylakoid membranes of chloroplasts (or the plasma membrane or internal membranes of bacteria).
     

    Light reactions

    • 2 photosystems
    • transfer of e- from H2O (in the lumen) to NADP+ (in the stroma)
    • transfer of H+ from stroma to lumen (and back through ATP synthase)