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part of the antenna complex to the inner part. This funneling of energy is performed via resonance transfer, which occurs when energy from an excited molecule is transferred to a molecule in the ground state. This ground state molecule will be excited, and the process will continue between molecules all the way to the reaction center. At the reaction center, the electrons on the special chlorophyll molecule will be excited and ultimately transferred away by electron carriers. (If the electrons were not transferred away after excitation to a high energy state, they would lose energy by fluorescence back to the ground state, which would not allow plants to drive photosynthesis.) The reaction center will drive photosynthesis by taking light and turning it into chemical energy that can then be used by the chloroplast.
31:
225:(a light harvesting complex or LHC) and a reaction center. The antenna complex is where light is captured, while the reaction center is where this light energy is transformed into chemical energy. At the reaction center, there are many polypeptides that are surrounded by pigment proteins. At the center of the reaction center is a special pair of chlorophyll molecules.
307:
When the electron reaches photosystem I, it fills the electron deficit of light-excited reaction-center chlorophyll P700 of PSI. The electron may either continue to go through cyclic electron transport around PSI or pass, via ferredoxin, to the enzyme NADP reductase. Electrons and protons are added
279:
molecule, which ionizes the chlorophyll and boosts its energy further, enough that it can split water in the oxygen evolving complex (OEC) of PSII and recover its electron. At the heart of the OEC are 4 Mn atoms, each of which can trap one electron. The electrons harvested from the splitting of two
151:
which will absorb light. The pigments which absorb light at the highest energy level are found furthest from the reaction center. On the other hand, the pigments with the lowest energy level are more closely associated with the reaction center. Energy will be efficiently transferred from the outer
80:
PSII will absorb red light, and PSI will absorb far-red light. Although photosynthetic activity will be detected when the photosystems are exposed to either red or far-red light, the photosynthetic activity will be the greatest when plants are exposed to both
299:) to pump protons across the membrane, into the thylakoid lumen space from the chloroplast stroma. This will provide a potential energy difference between lumen and stroma, which amounts to a proton-motive force that can be utilized by the proton-driven
193:
terminal electron acceptor. Both reaction center types are present in chloroplasts and cyanobacteria, and work together to form a unique photosynthetic chain able to extract electrons from water, creating oxygen as a byproduct.
243:. In the reaction center of PSII of plants and cyanobacteria, the light energy is used to split water into oxygen, protons, and electrons. The protons will be used in proton pumping to fuel the ATP synthase at the end of an
303:
to generate ATP. If electrons only pass through once, the process is termed noncyclic photophosphorylation, but if they pass through PSI and the proton pump multiple times it is called cyclic photophosphorylation.
99:
The main function of PSII is to efficiently split water into oxygen molecules and protons. PSII will provide a steady stream of electrons to PSI, which will boost these in energy and transfer them to NADP and
263:
are required for oxygenic photosynthesis. Oxygenic photosynthesis can be performed by plants and cyanobacteria; cyanobacteria are believed to be the progenitors of the photosystem-containing chloroplasts of
275:
At the core of photosystem II is P680, a special chlorophyll to which incoming excitation energy from the antenna complex is funneled. One of the electrons of excited P680* will be transferred to a non-
332:, the remaining oxygen species will be detrimental to the photosystems of the plant. More specifically, the D1 subunit in the reaction center of PSII can be damaged. Studies have found that
336:
proteins are involved in the degradation of these damaged D1 subunits. New D1 subunits can then replace these damaged D1 subunits in order to allow PSII to function properly again.
96:
molecules which funnel the excitation energy to the center of the photosystem. At the reaction center, the energy will be trapped and transferred to produce a high energy molecule.
324:
In intense light, plants use various mechanisms to prevent damage to their photosystems. They are able to release some light energy as heat, but the excess light can also produce
85:
of light. Studies have actually demonstrated that the two wavelengths together have a synergistic effect on the photosynthetic activity, rather than an additive one.
562:
Orf GS, Gisriel C, Redding KE (October 2018). "Evolution of photosynthetic reaction centers: insights from the structure of the heliobacterial reaction center".
182:
for PSI and 680 nanometers for PSII in chloroplasts), the amount and type of light-harvesting complex present, and the type of terminal electron acceptor used.
202:
A reaction center comprises several (about 25-30) protein subunits, which provide a scaffold for a series of cofactors. The cofactors can be pigments (like
992:
884:
803:
171:) in chloroplasts and in non-sulfur purple bacteria). The two photosystems originated from a common ancestor, but have since diversified.
105:
527:(November 2006). "Conservation of distantly related membrane proteins: photosynthetic reaction centers share a common structural core".
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89:
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of plants and algae, and in the cytoplasmic membrane of photosynthetic bacteria. There are two kinds of photosystems: PSI and PSII.
807:
798:
189:-like iron-sulfur cluster proteins as terminal electron acceptors, while type II photosystems ultimately shuttle electrons to a
58:
442:
466:
Gisriel, Christopher; Sarrou, Iosifina; Ferlez, Bryan; Golbeck, John H.; Redding, Kevin E.; Fromme, Raimund (2017-09-08).
62:
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725:"The Thylakoid Lumen Protease Deg1 Is Involved in the Repair of Photosystem II from Photoinhibition in Arabidopsis"
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to NADP to form NADPH. This reducing (hydrogenation) agent is transported to the Calvin cycle to react with
808:
Superfamily » 1.1.002. Photosystems (7 families) - Orientations of
Proteins in Membranes (OPM) database
958:
17:
155:
Two families of reaction centers in photosystems can be distinguished: type I reaction centers (such as
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108:. The hydrogen from this NADPH can then be used in a number of different processes within the plant.
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816:– Calculated spatial positions of photosynthetic reaction centers and photosystems in membrane
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and oxidize molecules (give off and take up electrons). This reaction center is surrounded by
613:
Caffarri, Stefano; Tibiletti, Tania; Jennings, Robert C.; Santabarbara, Stefano (June 2014).
524:
309:
479:
88:
Each photosystem has two parts: a reaction center, where the photochemistry occurs, and an
615:"A Comparison Between Plant Photosystem I and Photosystem II Architecture and Functioning"
8:
1109:
1099:
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280:
waters fill the OEC complex in its highest-energy state, which holds 4 excess electrons.
268:. Photosynthetic bacteria that cannot produce oxygen have only one photosystem, which is
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163:) in chloroplasts and in green-sulfur bacteria) and type II reaction centers (such as
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295:. Energy from PSI drives this process and is harnessed (the whole process is termed
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of plants, algae, and cyanobacteria. These membranes are located inside the
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377:"Far-red light is needed for efficient photochemistry and photosynthesis"
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247:. A majority of the reactions occur at the D1 and D2 subunits of PSII.
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468:"Structure of a symmetric photosynthetic reaction center–photosystem"
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Light-dependent reactions of photosynthesis at the thylakoid membrane
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Photosystem II: Molecule of the Month in the
Protein Data Bank
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Reaction centers are multi-protein complexes found within the
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Photosystem I: Molecule of the Month in the
Protein Data Bank
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to photosystem I via an electron transport chain within the
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Kapri-Pardes, Einat; Naveh, Leah; Adam, Zach (March 2007).
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Structural units of protein involved in photosynthesis
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Branched-chain alpha-keto acid dehydrogenase complex
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Each PSII has about 8 LHCII. These contain about 14
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Phosphoenolpyruvate sugar phosphotransferase system
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Photosystems I + II: Imperial
College, Barber Group
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561:
375:Zhen, Shuyang; Van Iersel, Marc W. (2017-02-01).
174:Each of the photosystem can be identified by the
147:In addition, surrounding the reaction center are
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914:Photosynthetic reaction center complex proteins
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822:"Photosystem II: evolutionary perspectives"
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328:. While some of these can be detoxified by
221:Each photosystem has two main subunits: an
178:of light to which it is most reactive (700
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826:Philos. Trans. R. Soc. Lond. B Biol. Sci
820:Rutherford AW, Faller P (January 2003).
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128:At the heart of a photosystem lies the
41:are functional and structural units of
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144:that enhance the absorption of light.
49:. Together they carry out the primary
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619:Current Protein & Peptide Science
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670:Jagannathan, B; Golbeck, JH (2009).
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239:molecules, as well as about four
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680:10.1016/B978-012373944-5.00352-7
434:Fundamentals of plant physiology
69:. Photosystems are found in the
1036:Carbamoyl phosphate synthase II
529:Molecular Biology and Evolution
1041:Aspartate carbamoyltransferase
949:Pyruvate dehydrogenase complex
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1073:Glycine decarboxylase complex
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283:Electrons travel through the
270:similar to either PSI or PSII
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394:10.1016/j.jplph.2016.12.004
381:Journal of Plant Physiology
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1146:Integral membrane proteins
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971:Oxoglutarate dehydrogenase
314:glyceraldehyde 3-phosphate
251:In oxygenic photosynthesis
142:light-harvesting complexes
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576:10.1007/s11120-018-0503-2
312:, along with ATP to form
198:Structure of PSI and PSII
1063:Electron transport chain
672:Photosynthesis:Microbial
245:electron transport chain
185:Type I photosystems use
1053:P450-containing systems
564:Photosynthesis Research
493:10.1126/science.aan5611
326:reactive oxygen species
1058:Cytochrome b6f complex
838:10.1098/rstb.2002.1186
741:10.1105/tpc.106.046573
523:Sadekar S, Raymond J,
431:Taiz, Lincoln (2018).
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898:multienzyme complexes
541:10.1093/molbev/msl079
310:glycerate 3-phosphate
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674:. pp. 325–341.
216:iron-sulfur clusters
61:and the transfer of
1110:Tryptophan synthase
1100:Polyketide synthase
799:Photosystem II: ANU
484:2017Sci...357.1021G
478:(6355): 1021–1025.
136:that uses light to
124:thylakoid membrane.
71:thylakoid membranes
59:absorption of light
320:Photosystem repair
293:thylakoid membrane
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387:: 115–122.
285:cytochrome
277:fluorescent
241:carotenoids
212:carotenoids
204:chlorophyll
94:chlorophyll
83:wavelengths
1125:Categories
453:1035316853
362:References
266:eukaryotes
208:pheophytin
187:ferredoxin
180:nanometers
176:wavelength
749:1040-4651
708:ignored (
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67:electrons
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340:See also
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104:to make
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810:at the
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580:OSTI
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449:OCLC
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399:ISSN
334:deg1
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169:P680
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1008:DBT
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