Friday, November 26, 2010

Light Reaction in Photosynthesis

  1. Happens = in photosystem (in thylakoid membrane).
  2. Involved only PSI (In cyclic photophosphorylation)
  3. Energised e-:
    • are released from the excited chlorophyll a (P700)
    • is picked up by a primary acceptor.
    • pass through electron transport chain
    • return to P700
    •  by releasing energy (to produce ATP from ADP and Pi).
    Cyclic photophosphorylation
    Involved both PSI and PSII (In non-cyclic photophosphorylation)
  5. Energised e- :
    • are released from the excited chlorophyll a (P680)
    • is picked up by the primary acceptor.
    • are transported to cytochrome complex
    • through the elcetron carrier plastoquinone 
    • during which its energy is trapped to form ATP.
  6. Electron hole:
    • is formed in P680 due to the transport of the excited electron
    • is filled up by the electron produced during photolysis.
  7. Low energy level e-:
    • from the cytochrome complex are transported to P700 through plastocyanin.
    • transportedfrom P700 to NADP for reduction (catalyzed by NADP+ reductase (enzyme)
    • via the primary acceptor and ferredoxin.
  8. Net energy gain (during non-cyclic photophosphorylation) = 1 mol ATP + 1 mol NADPH.
Non-cyclic photophosphorylation

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