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Updated on 02nd May, 2023 , 4 min read
Using light energy from photosynthesis, the process of photophosphorylation turns ADP into ATP. By transferring the phosphate group into the ADP molecule when it is illuminated, energy-dense ATP molecules are created. Two forms of photophosphorylation exist- Cyclic Photophosphorylation and Non-cyclic Photophosphorylation.
Non-cyclic photophosphorylation is the name given to the photophosphorylation procedure that causes the electrons to travel non-cyclically in order to synthesize ATP molecules using the energy from excited electrons supplied by photosystem II. Because P700 of Photosystem I takes up the lost electrons from P680 of Photosystem II and prevents them from being converted back to P680, this process is known as non-cyclic photophosphorylation. In this case, the whole movement of the electrons is unidirectional or non-cyclic.
The electrons generated by P700 during non-cyclic photophosphorylation are first transported by the main acceptor before being transferred to NADP. One ATP and two NADPH2 molecules are produced by non-cyclic photophosphorylation. Here, the water molecules' splitting produces protons (H+), which are coupled with the electrons to convert NADP into NADPH. The response is displayed below-
Non-cyclic electron transport/photophosphorylation is the electron transport sequence in which NADP+ is reduced by PSI, PSI is reduced by PSII, and lastly, PSII is reduced by electrons derived from photo-oxidation of water. As a result of the cycle being disrupted during this electrotransfer, it is referred to as non-cyclic. This kind of electron transport is linked to the photooxidation of water and the generation of molecular oxygen. It released a significant amount of protons, which eventually generated a proton motive force to manufacture ATP. Non-cyclic electron transport is critical in photosynthesis because it provides assimilatory power in the form of NADPH and ATP for CO2 assimilation while also purifying the ambient air.
A P700 (chlorophyll molecule) reaction center and a number of auxiliary pigments make up PS I. The PS I, or photosystem I, is linked to the following responses-
The two P700 reaction centers, each of which lost one electron, are unstable because of this. They are unable to absorb photon energy through the accessory pigments and are unable to release further electrons until the initially lost electrons have been replaced. Photosystem II now participates in the light response.
NADPH was created by the first known photosystem, photosystem I. The later-discovered new photosystem was given the name PS II. The following is the list of reactions of photosystem II-
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