Cyclic electron transport produces ATP but no NADPH

Noncyclic electron transport produces ATP and NADPH + H+. However, as we will see, the Calvin-Benson cycle uses more ATP than NADPH + H+. Cyclic electron transport occurs in some organisms when the ratio of NADPH + H+ to NADP+ in the chloroplast is high. This process, which produces only ATP, is called cyclic because an electron passed from an excited chlorophyll molecule at the outset cycles back to the same chlorophyll molecule at the end of the chain of reactions (Figure 8.10).

details of the reactions. The reactions of noncyclic electron transport from water to NADP+ are depicted in Figure 8.9. Photosystem II absorbs photons, sending electrons from P680 to the primary electron acceptor— the first carrier in the redox chain— and causing P680 to become oxidized to P680+. Electrons from the oxidation of water are passed to P680+, reducing it once again to P680, which can then absorb more photons. The electron from photosystem II passes through a series of exergonic reactions in the redox chain that are indirectly coupled across the thylakoid membrane to proton pumping. This pumping creates a proton gradient that produces energy for ATP synthesis.

In photosystem I, the reaction center containing P700 becomes excited to

1Ï In cyclic electron flow, excited electron transport and chlorophylls pass electrons to an oxidizing agent, ferredoxin, leaving positively charged chlorophyll (Chl +

1Ï In cyclic electron flow, excited electron transport and chlorophylls pass electrons to an oxidizing agent, ferredoxin, leaving positively charged chlorophyll (Chl +

Plasma Membrane Electron Transport

8.10 Cyclic Electron Transport Traps Light Energy as ATP Cyclic electron transport produces ATP, but no NADPH + H+.The same chlorophyll molecule passes on the electrons that start the reactions and receives the electrons at the end to start the process over again.

The last reduced electron carrier (plastocyanin) passes electrons to electron-deficient chlorophyll, allowing the reactions to start again.

8.10 Cyclic Electron Transport Traps Light Energy as ATP Cyclic electron transport produces ATP, but no NADPH + H+.The same chlorophyll molecule passes on the electrons that start the reactions and receives the electrons at the end to start the process over again.

The last reduced electron carrier (plastocyanin) passes electrons to electron-deficient chlorophyll, allowing the reactions to start again.

Before cyclic electron transport begins, P700, the reaction the redox chain by way of plastocyanin (PC), and comes back center chlorophyll of photosystem I, is in the ground state. It absorbs a photon and becomes P700*. The P700* then reacts with oxidized ferredoxin (Fdox) to produce reduced ferre-doxin (Fdred). The reaction is exergonic, releasing free energy. Reduced ferredoxin (Fdred) passes its added electron to a different oxidizing agent, plastoquinone (PQ, a small organic molecule), which pumps 2 H+ back across the thylakoid membrane. Thus, Fdred reduces PQ, and PQred passes the electron to a cytochrome complex (Cyt). The electron continues down the electron transport chain until it completes its cycle by returning to P700+, resulting in a restoration of its uncharged form, P700. By the time the electron from P700* travels through

Bacterial Electron Transport Chain

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Responses

  • Jorma Aalto
    What produces atp but no nadph?
    8 years ago
  • eglantine
    What creats nadph in electron chain process?
    7 years ago
  • RENATO
    How is the electron from p680 restored?
    7 years ago
  • Kasey
    How cyclic electron flow generates ATP But no NADPH?
    3 years ago

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