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Non-cyclic Electron Transport in Photosynthesis

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 ).

Three series of exposures were carried out, beginning at selected times after hatching.

31The oxidation state of ferredoxin provides a gauge of the rate ofphotosynthesis. When the pool of ferredoxin is mostly reduced (as it is soon after a dark light transition), some of the electrons are not used for thereduction of NADP+; instead, they reduce proteins called thioredoxins. Theseproteins, in turn, reduce disulfides on target proteins to sulfhydryls. Notably, Glc 6-Pdehydrogenase (the "entry point" to the OPPP) is thus inactivated. The RPPP isthus activated (e.g., P-ribulokinase, PGal dehydrogenase, and the well studied P'ases). Aswe discussed during membrane transport, primary ion pumps can function as either ion pumpsor as ATP synthases, depending on the energetics. As there is only a small pH across the thylakoid membranes indarkness, the energetics would favor "wasteful" ATP hydrolysis. It is thereforenecessary that this electroenzyme be regulated. One mechanism that is involved in thelight-activation of this pump is thioredoxin-mediated.

Cyclic Electron Transport in Photosynthesis

After passing through a series of electron carriers, the last step in the process is the reduction of NADP+ to NADPH.

The compounds used to carry electrons include pheophytin (chlorophyll without the magnesium ion (Mg2+) center), quinones, cytochromes, plastocyanins (copper-containing proteins), nonheme iron sulfur proteins, ferredoxin, and flavoproteins.

Oxygenic photosynthesis occurs in, among others, eukaryotic microorganisms like algae and in bacteria such as cyanobacteria; the same mechanism is at work in both. Electron flow happens through two different electron transport chains that are connected; together, these electron transport chains are called the . The stars of each chain are photosystem I (PSI) and photosystem II (PSII), each containing chlorophyll reaction centers surrounded by antenna pigments.

Cyclic and noncyclic photophosphorylation ..

Cyclic DiagramConnections to Electron FlowBoth cyclic and noncyclic photophosphorylation have an electron flow.

Electrons cycle back to reduce P870, so this is a cyclic electron transport chain leading to generation of ATP through cyclic photophosphorylation.

Some of the carriers within the electron chain are different, including bacteriopheophytin, which is bacteriochlorophyll without its Mg2+ ion.

This may have a mechanism similar to the interference by ammonium ion with electron transfer in the photosynthetic reaction.
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Noncyclic Electron Transport - YouTube

The b-f complex acts as an inter-photosystem electron carrier. We are not entirelycertain of the mechanism of electron and proton flow through this complex, althoughanalogous processes in the similar complexes of bacteria and mitochondria are welldescribed. Because of time pressures, we will not focus on this complex; the"product" is plastocyanin , the seconddiffusible intermediate. Plastocyanin is a small protein ( ~10 KD) that forms the redoxconnection between b-f complex and PSI.

03/11/2014 · Noncyclic Electron Transport CHSWinkler

1Cyanobacteria and all photosynthetic eukaryotes conduct"oxygenic" photosynthesis. I.e., they extract electrons from H2O andthe byproduct is O2. Although I have referred to this as photosynthesis withoutqualification, you should at least be aware that some prokaryotes utilize other than H2Oas an electron donor. As an example, one taxon extracts electrons from H2S; theproduct, elemental S, is found in large deposits owing to these organisms, just as O2in the atmosphere accumulated from oxygenic organisms. We will not discuss non-oxygenicphotosynthesis, except in a historical context, in this course in plantphysiology. However, as we have stressed, biochemistry is very similar among allorganisms. Indeed, important insights into plant photosynthesis have come from studieswith bacteria. The first integral membrane protein to be crystallized is a part of thephotosynthetic machinery of a non-oxygenic photosynthetic bacterium. The crystallizationpermitted detailed structural analysis. As an unabashed plant chauvinist, I would take theposition that this work was most important because inferences about the structure of partof the photosynthetic machinery ("Photosystem II") of plants could be drawn fromthis bacterium's photosynthetic apparatus. This work was recognized by a 1988 Nobel Prize(to Michel and Deisenhofer, of München). (A not-so-subliminal message is that advances inunderstanding often rely on technical advancesin this case,protein crystallization. You will recall the importance of the patch-clamp technique toinvestigations of membrane transport. This work, too, was recognized by a Nobel Prize (toNeher, of Göttingen).)

Cyclic & Noncyclic Electron Flow - Duration: ..

The reduction of QB to the hydroquinone requires not only electrons, butprotons, also. These protons are taken up from the stromal side of the membrane. When QBis oxidized by a complicated cycle, a total of four (?) H+s are released intothe lumen. This contribution to the pH is thesecond energy conservation site. QB is the first of two mobile carriers that wewill discuss.

Cyclic vs. Non-cyclic Electron Flow - Mandeville High …

We turn now, for summary and orientation to the overall process of photosyntheticelectron transport, to the fourth and final topic, i.e., a functional description of howthree of the four major protein complexes function to transport electrons from H2Oto NADP+.

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