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What is non-cyclic photophosphorylation?

 Non-cyclic photophosphorylation begins when a water molecule is broken down by a process called photolysis. Next, a photon is absorbed and the light causes a chain reaction that transfers energy to the core. This in turn excites the two electrons transferred to pheophytin. Taking electrons from another molecule of water makes up this deficit. These electrons transfer from pheophytin to plastoquinone and once further broken down, are released. Two H+ ions are then released and the electrons then through Cyt b6 and Cyt f, and then through plastocyanin. This creates a gradient, which provides the energy for regeneration of ATP.

 ·  When photosystem II absorbs light, an electron excited to a higher energy level in the reaction center chlorophyll (P680) is captured by the primary electron acceptor.  The oxidized chlorophyll is now a very strong oxidizing agent; its electron “hole” must be filled.

·  An enzyme extracts electrons from water and supplies them to P680, replacing the electrons that the chlorophyll molecule lost when it absorbed light energy.  This reaction splits a water molecule into two hydrogen ions and an oxygen atom, which immediately combines with another oxygen atom to form O₂.  This splitting of water is responsible for the release of O₂ into the air.

·  Each photoexcited electron (energized by light) passes from the primary electron acceptor in photosystem II to photosystem I via an electron transport chain.  This electron transport chain is very similar to the one in cellular respiration; however, the carrier proteins in the chloroplast ETC are different from those in the mitochondrial ETC.

·  As electron move down the chain, their exergonic “fall”to a lower energy level is harnessed by the thylakoid membrane to produce ATP (by chemiosmosis).  The production of ATP in the chloroplast is called photophosphorylation because the energy harnessed in the process originally came from light.  This process of ATP production is called non-cyclic photophosphorylation.  The ATP generated in this process will provide the energy for the synthesis of glucose during the Calvin cycle (light independent reactions).