Cyclic Electron Transport in Photosynthesis

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).

Photosynthesis - Cyclic Electron ..

McGraw-Hill Flash animation illustrating cyclic and non-cyclic photophosphorylation.

Photosynthesis Non Cyclic Photophosphorylation - …

Cyclic electron flow avoids both and the donation of electrons to +. instead are passed from to an , resulting in , and then returned to , returning that to its ground state. Also can be described as a .

This cyclical process is rather than those being originally sourced from . The process is described as cyclical because rather than flowing from one component of the to another ( to +), they instead cycle back to the same component ( to ).

Cyclic Electron Flow - Biology As Poetry

The effect of cyclic electron flow is simply the diversion of more captured to production than otherwise would be the case with alone. The reason for this diversion is simply that more is required to complete than is generated relative to production by alone.

Cyclic and Noncyclic Photophosphorylation HD Animation ..

In respiration energy is released fromsugars when electrons associated with hydrogen are transported to oxygen (theelectron acceptor), and water is formed as a byproduct. The mitochondriause the energy released in this oxidation in order to synthesize ATP. Inphotosynthesis, the electron flow is reversed, the water is split (not formed),and the electrons are transferred from the water to CO2 and in theprocess the energy is used to reduce the CO2 into sugar. Inrespiration the energy yield is 686 kcal per mole of glucose oxidized to CO2,while photosynthesis requires 686 kcal of energy to boost the electrons from thewater to their high-energy perches in the reduced sugar -- light provides thisenergy.

Cyclic Photophosphorylation - YouTube

Both the LHC and the reaction centers are membrane bound structures but there are no chloroplasts in the purple photosynthetic bacteria. The electron transfer processes occur within the cell membrane and the overall process is a cyclic one (i.e., there is no net oxidation-reduction). Protons are transferred across the membrane, from the cytoplasmic side to the outside, establishing a proton gradient whose dissipation drives ATP synthesis. A similar situation holds for the cyanobacteria and plants, but in these organisms, the process occurs in chloroplasts and the overall reaction is not a cyclic one.

Light reaction of photosynthesis Cyclic and non cyclic ..

Chapter 22 ("Electron Transport and Oxidative Phosphorylation") in Voet & Voet (3rd Edition) is one of the most important chapters in the entire text (at least in my opinion) and it would help to reread it as you look at the light reaction of photosynthesis in more detail over the next two lectures.

Cyclic and Noncyclic Photophosphorylation

The most common light-dependent reaction in photosynthesis is called noncyclic photophosphorylation. Noncyclic photophosphorylation involves both Photosystem I and Photosystem II and produces ATP and NADPH. During noncyclic photophosphorylation, the generation of ATP is coupled to a one-way flow of electrons from H2O to NADP+.

Noncyclic Photophosphorylation - YouTube

(3) Exciton Transfer (Resonance Energy Transfer): Transfer of energy to a nearby unexcited molecule with similar electronic properties. This can happen because the molecular orbital energy levels of the molecules overlap. This mechanism will play an important role in photosynthesis.