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explain cyclic photophospho relation with the help of diagramatic representation

Dear student,

Photo-Phosphorylation

  • The process of formation of ATP in chloroplast in the presence of sunlight

  • Photo-phosphorylation is of two types:

    • Non-cyclic photo-phosphorylation

    • Cyclic photo-phosphorylation

Cyclic Photo-Phosphorylation

  • In this scheme, only PSI is functional. Hence, the electrons are circulated within the photosystem.

  • This results in a cyclic flow of electrons.

  • This scheme could possibly be occurring in stroma lamellae because it lacks both PSII and NADP reductase enzyme.

  • This cyclic flow results only in the synthesis of ATP, and not of NADPH + H+.

    Regards

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Cyclic photophosphorylation-
  1. PS-I absorbs energy of different wavelength and funnels it to the reaction center.
  2. P700 gets excited and loses an electron which is accepted by the iron containing red protein called ferredoxin through an unknown electron acceptor called ferredoxin reducing substance (FRS). Thus the reaction center gets ionized or positively charged.
  3. The energized electron rolls down a number of electron carriers like cytochrome b6, cytochrome f and plastocyanin. Reduced plastocyanin transfers the denergized electron to the reaction center of PS-I. Hence, the lost electron comes comes back to the reaction center.
  4. While transfer of electron from cyt b6 to cyt f, the energy released is used in the synthesis of ATP. ATP is also syntesized when the electron is transfered from cyt f to plastocyanin.
  5. Cyclic photophosphorylation is a significant process since extra ATP is synthesized which is required for dark reaction.
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