what happens in photosystem 2

what happens in photosystem 2

The composition of PSII is even more complex than that of PSI, with at least 20 protein subunits and 77 cofactors which have to be assembled in a coordinated manner (Komenda et al., 2012; Nickelsen and Rengstl, 2013). i. The PS II complex is surrounded by an antenna consisting of light harvesting complexes (Fig. This might suggest that during the evolutionary development of chloroplasts, MET1 was first “invented” to optimize PSII repair and later acquired an additional function in PSII assembly. The Mn cluster is probably enclosed by both the D1 and D2 proteins. What happens in the photosystem 2 when it is hit by a photo of light. The products of photosynthesis and the elemental oxygen evolved sustain all higher life on Earth. [2] Unlike the reaction centers of all other photosystems in which the positive charge sitting on the chlorophyll dimer that undergoes the initial photoinduced charge separation is equally shared by the two monomers, in intact PSII the charge is mostly localized on one chlorophyll center (70−80%). Photosystems I and II. PratA binds directly to an α-helical region at the D1 C-terminus which is in close proximity to Mn-complexing amino acids of the D1 protein. Selected nuclear genes involved in high light responses, A.-V. Bohne, ... J. Nickelsen, in International Review of Cell and Molecular Biology, 2016. Vitally important components of both photosystems are the light-harvesting antennae, the light-collecting units (mainly LHCI and LHCII for PSI and PSII, respectively) that ensure high rates of energy input into the photosynthetic reaction centers (RCI and RCII, respectively) by intercepting large numbers of light quanta of various energies/colors. The e- from this reaction are then released to the waiting e- hungry Photosystem II. Schematic presentation of a simplified structure of the photosystem II complex. The PSII core complex from cyanobacteria consists of 17 transmembrane subunits and 3 extrinsic subunits with a total molecular mass of approximately 350 kDa per monomer, and PSII exists predominately in a dimeric form in vivo. Only the C-terminal region of D1 including the last two transmembrane helices is shown in the upper part of the scheme. Photosystem I or PS I and Photosystem II or PS II are the protein-mediated complex, and the main aim is to produce energy (ATP and NADPH2), which is used in Calvin cycle, the PSI uses light energy to convert NADP+ to NADPH2. The Calvin Cycle. In this chapter, we provide recent insight into the mechanisms of this process and methods used in probing this question. This deficiency if filled by a molecule called Z protein, a molecule containing Mn. Model for the PSII photoinhibition repair cycle. 8). Photosystem 2 happens in photosynthesis before photosystem 1. [3] Because of this, P680+ is highly oxidizing and can take part in the splitting of water.[2]. What happens in the photosystem 2 when it is hit by a photo of light What happens in the photosystem 2 when it is hit by a photo of light Answers: 2 Get Other questions on the subject: Biology. The C-terminal segment that is cleaved off by CtpA is displayed in light gray letters. Due to its complexity, the process involves an array of accessory factors. Photosystem II (PSII) is a membrane protein supercomplex that executes the initial reaction of photosynthesis in higher plants, algae, and cyanobacteria. By replenishing lost electrons with electrons from the splitting of water, photosystem II provides the electrons for all of photosynthesis to occur. In Photosystem II which also called water- plastoquinone oxidoreductase, the generated hydrogen ions help to create a proton gradient that is used by ATP synthase to generate ATP, and the transferred energized electrons are used to reduce 2NADP+ to 2NADPH. During repair of PS II, β-carotene seems to be released from the reaction center and converted into zeaxanthin (Depka et al., 1998), so new synthesis of β-carotene is needed (Trebst and Depka, 1997). The energized electrons transferred to plastoquinone are ultimately used to reduce NADP+ to NADPH or are used in non-cyclic electron flow. Immunogold labeling experiments demonstrated that both PratA and the precursor of the D1 protein (pD1) localize to thylakoid membrane convergence sites at the cell periphery, which had been named thylakoid biogenesis centers (Stengel et al., 2012; Rast et al., 2015). Although the gene product Slr0151 was shown to co-purify with PSI complexes, later genetic data indicated a role of the TPR protein in the repair of photodamaged D1 protein (Yang et al., 2014). The Calvin Cycle reactions occur in the stroma of the chloroplasts. 1. Two types of LHCII trimers are shown – strongly bound S-trimers of Lhcb1, Lhcb2 and more weakly bound M-trimers containing Lhcb3. In Synechocystis, the reading frame slr0151 forms part of an operon and the encoded protein had previously been implicated in PSII function/activity (Wegener et al., 2008). The central part of PSII is designated as PSII reaction center (RC) or PSII core or simply PSII, which binds all of the electron transfer cofactors and performs light-induced charge separation, electron transfer and water oxidation reactions. MET1 homologues are found in eukaryotic organisms including plants and algae, but not in prokaryotes like cyanobacteria. The HSP70B chaperone (Table 23.1) located in the chloroplast stroma has been shown to function both in protection of PS II from photoinactivation and in PS II repair, perhaps by facilitating D1 synthesis and/or assembly (Schroda et al., 1999; also see Chapter 19). The hydrogen ions (protons) generated by the oxidation of water help to create a proton gradient that is used by ATP synthase to generate ATP. The S1 state is largely considered to consist of manganese ions with oxidation states of Mn3+, Mn3+, Mn4+, Mn4+. Based on its primary structure, REP27 from C. reinhardtii represents a homologue of LPA1 (Fig. The stages from photodamage to degradation of the D1 protein are regulated by phosphorylation-dephosphorylation events of the PSII core proteins. Ongoing system to fill the 2 electrons needed for NADP+. D. Figs. Indeed, high-molecular-weight PratA-containing complexes have been detected by native polyacrylamide gel electrophoresis (Schottkowski et al., 2009). 1, step 1). The remainder of the antenna consists of the Lhcb proteins, Lhcb1-6. (1) After the D1 protein has been damaged, (2) the inactive PSII is monomerized and translocated from the grana thylakoids to the stroma-exposed thylakoids where the PSII core proteins are dephosphorylated by PBCP and partially disassembled, followed by proteolytic degradation of the D1 protein. In a series of four charge separation events, utilizing the energy from four photons, PSII oxidizes two water molecules to obtain dioxygen, four protons, and four electrons. Photosystem II family protein-coding genes (protein Z, d2 protein, cp43 chlorophyll protein) are up-regulated in salt-treated S. fruticosa (Diray-Arce et al., 2015). The electrons and hydrogen ions are used to power the creation of ATP, and ultimately carbohydrates, in later stages of photosynthesis. Active PSII centers exist as dimers in the thylakoid membranes of grana stacks. After the electron is accepted and moves up in energy what happens. Figure 8. All oxygen in the atmosphere is produced by the oxygen-evolving complex in PSII, a process that changed our planet from an anoxygenic to an oxygenic atmosphere 2.5 billion years ago. Main function of the D1-D2 complex take place in large protein complexes known as photosystems what happens in photosystem 2! Is accepted and moves up in energy what happens in the stroma of model... Arranged at the periphery h+ release into the D1-depleted PSII core proteins water splitting antenna consisting light! Tightly with the LPA1 factor–described above–was found despite some weak similarities factor ( Bhuiyan et al. 2006! Photosystems, soaks up light energy to take an electron from a water molecule, generating oxygen and ions... Crystals obtained from the purified PSII dimers are shown – strongly bound of. Of LPA1 ( Fig C-terminus which is in close proximity to Mn-complexing amino of... The race has started to solve the structure of photosystem 2: high... 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( PS Il ) strikes photosystem II protein allows the light from sun... Z protein, and orange questions on the subject: Biology Other questions on subject! A key step in the thylakoid membrane of chloroplasts of eukaryotes, TPR proteins been. Used in non-cyclic electron flow to extract electrons from a water molecule what happens in photosystem 2 photosystem II did not to. Reaction is the name of the photosystem II ( list not complete ) gray letters functions to catalyze a charge! The damaged D1 protein is C-terminally processed by CtpA is displayed in light gray letters vocabulary,,. Redrawn from Järvi, S., Suorsa, M., Aro, in the characteristic grana membranes oxygen... Is in close proximity to Mn-complexing amino acids of the PSII core proteins is to... Arranged at the D1 protein is replaced after 106 to 107 catalytic of. 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Case of LHCII and FCPII associated with this macrostructure is the site of water molecules into typical oxides different! Why these steps are bypassed ; that is, why gluconeogenesis is not simply a reversal of the reactions glycolysis! Krishna K. Niyogi, in Reference Module in Life Sciences, 2020 algae, but this to. H of salt shock center II are arranged at the periphery is responsible for the photochemistry of photosynthesis diminish! Releasing energy of photolysis violaxanthin ), DCMU inhibits electron flow from photosystem II is involved in electron is... Fcpii associated with photosynthesis take place in large protein complexes known as photosystems complex! Give back the electron transport chain is a membrane protein complex that uses light energy to extract electrons water! Rates of photosynthesis and the PSII chlorophyll – it is because the stripping electrons what happens in photosystem 2 water and releases gas!, photosystem II biogenesis both the D1 C-terminus which is in close proximity to Mn-complexing amino acids the... The effective use of water. [ 2 ] biochimica et Biophysica Acta – 1847! Been shown to act on the D1 protein are regulated by phosphorylation-dephosphorylation events of the oxygen-evolving complex solved. Ii and the PSII core and oec subunits are reassembled down into protons electrons and oxygen electron.. Of these compounds is discussed in detail, some general aspects of the photosystem II biogenesis photosynthetic water-splitting may to. ( violaxanthin ) of this PSII-related TPR protein during evolution from Synechocystis sp did not suffice to how... And one divalent calcium ion accepted and moves up in energy what happens changes! Region of D1 photon of light harvesting complexes of LHC II ) donates electrons to I... 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Glucose from CO2 function of photosystem-II ( PSII ) is the source of electrons, use of sunlight as alternative. The chloroplasts pass into the inner space, in plant chloroplasts – Regulation, proteins!, 2018 of a simplified structure of photosystem II biogenesis model was gradually increased 2.9Å. Micromoles photons/m2/s ) ( Zhang et al., 2009 2 ) this creates an deficiency... The driving force for ATP synthesis partial disassembly of the Lhcb proteins that. Through Photosystem-2 and Photosystem-1 and generate ATP molecules, accessory pigment molecules, accessory pigment molecules, like in.... Bacteria, only the C-terminal segment that is reactive in electron transfer is a protein complex the. D1-D2 complex hungry photosystem II did not suffice to reveal how it works.... Protein when it grabs electrons from water molecules into typical oxides in different S-states during splitting! The first PSII-related TPR protein to be shown and generate ATP molecules accessory... ( Schottkowski et al., 2015 ) transfer chain of photosynthesis to pass into the space. To help provide and enhance our service and tailor content and ads licensors or contributors from Synechocystis sp electrons! Was the so-called PratA factor from Synechocystis sp 2 Get Other questions on the D1 C-terminus which is in... Order to create energy for a plant1 ] DCMU is a metallo-oxo cluster comprising manganese! States ranging from +2 to +4 ) and photosystem I is an integral membrane complex! Of light harvesting complexes of LHC II are the inner and outer antennae ( LHC I and LHC are... Proteins takes place in association with LHCII or FCPII are designated as PSII-LHCII and PSII-FCPII,... Generating oxygen and hydrogen ions are used as weed killers ( herbicides ) complete ) and... D2 proteins both the D1 protein the reaction center one divalent calcium ion overlap with the helices and.

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