Cyclic vs. Non-cyclic Electron Flow - Mandeville High …
Cyclic Electron Flow in Photosynthesis? | Yahoo Answers
Cyclic photophosphorylation occurs less commonly in plants than noncyclic photophosphorylation, most likely occurring when there is too little NADP+ available. It is also seen in certain photosynthetic bacteria. Cyclic photophosphorylation involves only Photosystem I and generates ATP but not NADPH. As the electrons from the reaction center of Photosystem I are picked up by the electron transport chain, they are transported back to the reaction center chlorophyll. As the electrons are transported down the electron transport chain, some of the energy released is used to pump protons across the thylakoid membrane from the stroma of the chloroplast to the thylakoid interior space producing a proton gradient or . As the accumulating protons in the thylakoid interior space pass back across the thylakoid membrane to the stroma through ATP synthetase complexes, this energy is used to generate ATP from ADP and Pi (see Fig. 4).
Cyclic Electron Flow in Photosynthesis
All phototrophic bacteria are capable of performing cyclicphotophosphorylationas described above and in Figure 16 and below in Figure 18. Thisuniversalmechanism of cyclic photophosphorylation is referred to as PhotosystemI. Bacterial photosynthesis uses only Photosystem I (PSI), but themore evolved cyanobacteria, as well as algae and plants, have anadditionallight-harvesting system called Photosystem II (PSII). Photosystem IIis used to reduce Photosystem I when electrons are withdrawn from PSIforCO2 fixation. PSII transfers electrons from H2Oandproduces O2, as shown in Figure 20.
Photosynthesis - Non cyclic Photophosphorylation - YouTube
These electron flows prevent the Photosystems from fully reducing all the electron carriers and causing photosynthesis to stop.
Instead, electrons can be donated to cytochrome bf instead of NADP.
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