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Photosynthèse

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Photosynthesis The process of photosynthesis produces ATP from ADP and Pi by using the energy from light to excite electrons that are passed along an electron transport chain. Coupled with the transfer of electrons is the pumping of hydrogen ions and the splitting of water molecules. The following complexes are found in the photosynthesis electron transport chain: Photosystem II, Cytochrome b6f, Photosystem I, Ferredoxin NADP Reductase (FNR), and the complex that make ATP... ATP Synthase. In addition to the complexes, tree mobile carriers are also involved: Plastoquinone Qb, Plastocyanin, and Ferredoxin. Other key components include photons, chlorophyll Molecules, Protons, Water, Molecular oxygen, NADP+, and the electron to form an NADPH, ...and ADP and Pi which can combine to form ATP. Photosynthesis occurs in the chloroplast of plants and algea. The process is also found in single cell organisms such as cyanobacteria that do not have chloroplast. Like its mitochondria counterpart, the chloroplast electron transport chain consist of several protein complexes and to mobile electron carriers. First, a photon of light hits a chlorophyll molecule surrounding the photosystem II complex. This creates resonance energy that is transferred to neighbouring chlorophyll molecule. When this energy reaches the reaction center imbedded in photosystem II, an electron is released. The reaction center chlorophyll contains electrons that can be transferred when excited. One photon is needed to excite each of the electrons in this chlorophyll. Once excited, two electrons are transferred to plastoquinone Qb, the first mobile carrier. In addition to the two electrons, Qb also picks up two protons from the stroma. The two electrons lost from the photosystem II are replaced by the splitting of water molecules. Water splitting also releases hydrogen ions into the lumen. This contribute to hydrogen ion gradient, similar to the one created by mitochodrial electron transport. After two water molecules have been split, one molecule of molecular oxygen is created. Plastoquinone Qb then transfers the two electrons to the cytochrome b6f complex. The two protons it picked up are released into the lumen. These transfers are coupled with the pumping of two more hydrogen ions into the lumen space by cytochrome b6f. The electrons are next transferred to plastocyanin, another mobile carrier. Next, the electrons are transferred from plastocyanin to photosystem I complex. It is here that photons again energise each electron propel their transfer to ferrodoxin. Ferredoxin then transfers the electrons to the ferredoxin NADP+ reductase, also known as FNR. After two electrons are transferred to FNR, NADPH is made by adding the to electrons and the hydrogen ion two NADP. The gradient created by the electron transport chain is utilised by the ATP synthase to create ATP from ADP and Pi. This is similar to the way ATP is synthesized in mitochondria. ATP, NADPH and molecular oxygen are the final vital produces of photosynthesis.

Video Details

Duration: 5 minutes and 2 seconds
Year: 2007
Country: United States
Language: English
Producer: World wide web institutionnal commitee
Views: 530
Posted by: bernardlasnier on Dec 7, 2009

Un documentaire d'animation résumant la phase lumineuse de la photosynthèse

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