Photosystem II: Difference between revisions
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< | <StructureSection load='3a0b' size='350' caption='Photosystem II, [[3a0b]]' scene='' > | ||
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==Background== | ==Background== | ||
This structure of Photosystem II was crystallized from the cyanobacteria, ''Thermosynechococcus elongatus'', at 3.0Å <ref> | This structure of '''Photosystem II''' was crystallized from the cyanobacteria, ''Thermosynechococcus elongatus'', at 3.0Å <ref>PMID: 16355230</ref> and at 3.50 Å <ref name="Archit">PMID: 14764885</ref>. PDB codes are [[2axt]] and [[1s5l]], respectively. Cyanobacteria and plants both contain Photosystem II while photosynthetic bacteria contain the bacterial reaction center. This photosynthetic protein complex is associated with a variety of functional ligands. It is a <scene name='Photosystem_II/Psii_dimer/1'>dimer</scene> composed mainly of alpha-helices. Nineteen <scene name='Photosystem_II/Protein_only/1'>subunits</scene> are in each monomer, with multiple extrinsic subunits associated with the oxygen evolving complex missing from this crystallization. Photosystem II is a membrane bound protein complex that in plants is associated with the thylakoid membrane of chloroplasts. <scene name='Photosystem_II/Hydrophobic_polar/1'>Polar and hydrophobic</scene> regions correlate with membrane associated nature of the protein. '''<span style="color:gray;background-color:black;font-weight:bold;">Hydrophobic</span>''' helices make up the transmembranal portion, while '''<FONT COLOR="#C031C7">polar</FONT>''' residues are concentrated externally on either side of the membrane. | ||
==Photosynthesis== | ==Photosynthesis== | ||
Photosystem II is an integral part of photosynthesis, the conversion of light energy into chemical energy by living organisms. Photosystem II is linked to a variety of other proteins, including Photosytem I. These proteins ultimately produce NADPH and ATP that power the Calvin cycle. Using this energy, glucose is synthesized from carbon dioxide and water. | Photosystem II is an integral part of photosynthesis, the conversion of light energy into chemical energy by living organisms. Photosystem II is linked to a variety of other proteins, including Photosytem I. These proteins ultimately produce NADPH and ATP that power the [[Calvin cycle]]. Using this energy, glucose is synthesized from carbon dioxide and water. See also [[Photosynthesis]]. | ||
==Electron Transfer== | ==Electron Transfer== | ||
[[Image:Chlorophyll_a.svg.png|thumb|170px|left|structure of chlorophyll ''a'']] | [[Image:Chlorophyll_a.svg.png|thumb|170px|left|structure of chlorophyll ''a'']] | ||
<scene name='Photosystem_II/Chlorophyll_green/4'>Chlorophyll</scene> surround Photosystem II and capture energy from sunlight, exciting electrons. Chlorophyll are highly conjugated and absorb visible light, along with accessory light harvesting pigments such as <scene name='Photosystem_II/Betacarotene/3'>beta carotene</scene>. Beta carotene absorbs visible light of other wavelengths and also protects Photosystem II by destroying reactive oxygen species that result from this photoexcitation. | <scene name='Photosystem_II/Chlorophyll_green/4'>Chlorophyll</scene> surround Photosystem II and capture energy from sunlight, exciting electrons. Chlorophyll are highly conjugated and absorb visible light, along with accessory light harvesting pigments such as <scene name='Photosystem_II/Betacarotene/3'>beta carotene</scene>. Beta carotene absorbs visible light of other wavelengths and also protects Photosystem II by destroying reactive oxygen species that result from this photoexcitation. Electrons are passed from chlorophyll to <scene name='Photosystem_II/Pheophytin_purple/5'>pheophytin</scene>. Pheophytin are very similar to chlorophyll except they contain 2 H<sup>+</sup> instead of a Mg<sup>2+</sup> ion. From the pheophytin, electrons transferred to <scene name='Photosystem_II/Quinone_pink/5'>plastoquinones</scene>, which are reduced. Located between each pair of quinones, an iron helps to transfer the electron. These plastoquinones eventually move to a plastoquinone pool which travels to another large protein subunit, cytochrome b <sub>6</sub>/ f. Eventually these electrons reduce NADP<sup>+</sup> to NADPH. The <scene name='Photosystem_II/Electron_pathway/3'>electron pathway</scene> through Photosystem II is shown, with '''<span style="color:orange;background-color:black;font-weight:bold;">beta-carotenes</span>''', '''<FONT COLOR="#571B7e">pheophytins</FONT>''', '''<FONT COLOR="#E42217">iron</FONT>''' and '''<FONT COLOR="#F535AA">plasotoquinones</FONT>'''. | ||
{{Clear}} | |||
==Oxygen Evolution== | ==Oxygen Evolution== | ||
Another important facet of Photosystem II is its ability to oxidize water to oxygen with its <scene name='Photosystem_II/Oxygen_evolving_centers/11'>oxygen evolving centers</scene>. These centers are <scene name='Photosystem_II/ | Another important facet of Photosystem II is its ability to oxidize water to oxygen with its <scene name='Photosystem_II/Oxygen_evolving_centers/11'>oxygen evolving centers</scene>. These centers are <scene name='Photosystem_II/Single_oxygen_evolving/1'>cubane-like</scene> structures with 3 '''<FONT COLOR="#8D38C9">manganese</FONT>''', 4 '''<FONT COLOR="#C11B17">oxygen</FONT>''' and a '''<span style="color:lime;background-color:black;font-weight:bold;">calcium</span>''' linked to a fourth manganese<ref name="Archit" />. Oxidation of water leaves 2 H <sup>+</sup> on the lumenal side of the membrane, helping to establish the proton gradient essential for ATP synthesis in the CF<sub>1</sub>CF<sub>0</sub>-ATP sythase protein. | ||
[[Image:b-car.svg.png|b-car.svg.png|thumb|left|400px|structure of beta carotene]] | |||
[[Image:plastoquinone.jpg|thumb|300px|left|reduced plastoquinone]] | |||
==3D structures of photosystem II== | |||
[[Photosystem II 3D structures]] | |||
</StructureSection> | |||
==Additional Resources== | |||
For additional information, see: [[Photosynthesis]] | |||
<br /> | |||
==References== | ==References== | ||
<references/> | <references/> | ||
[[Category:Topic Page]] | |||
Latest revision as of 12:02, 30 August 2023
BackgroundThis structure of Photosystem II was crystallized from the cyanobacteria, Thermosynechococcus elongatus, at 3.0Å [1] and at 3.50 Å [2]. PDB codes are 2axt and 1s5l, respectively. Cyanobacteria and plants both contain Photosystem II while photosynthetic bacteria contain the bacterial reaction center. This photosynthetic protein complex is associated with a variety of functional ligands. It is a composed mainly of alpha-helices. Nineteen are in each monomer, with multiple extrinsic subunits associated with the oxygen evolving complex missing from this crystallization. Photosystem II is a membrane bound protein complex that in plants is associated with the thylakoid membrane of chloroplasts. regions correlate with membrane associated nature of the protein. Hydrophobic helices make up the transmembranal portion, while polar residues are concentrated externally on either side of the membrane. PhotosynthesisPhotosystem II is an integral part of photosynthesis, the conversion of light energy into chemical energy by living organisms. Photosystem II is linked to a variety of other proteins, including Photosytem I. These proteins ultimately produce NADPH and ATP that power the Calvin cycle. Using this energy, glucose is synthesized from carbon dioxide and water. See also Photosynthesis. Electron Transfer surround Photosystem II and capture energy from sunlight, exciting electrons. Chlorophyll are highly conjugated and absorb visible light, along with accessory light harvesting pigments such as . Beta carotene absorbs visible light of other wavelengths and also protects Photosystem II by destroying reactive oxygen species that result from this photoexcitation. Electrons are passed from chlorophyll to . Pheophytin are very similar to chlorophyll except they contain 2 H+ instead of a Mg2+ ion. From the pheophytin, electrons transferred to , which are reduced. Located between each pair of quinones, an iron helps to transfer the electron. These plastoquinones eventually move to a plastoquinone pool which travels to another large protein subunit, cytochrome b 6/ f. Eventually these electrons reduce NADP+ to NADPH. The through Photosystem II is shown, with beta-carotenes, pheophytins, iron and plasotoquinones. Oxygen EvolutionAnother important facet of Photosystem II is its ability to oxidize water to oxygen with its . These centers are structures with 3 manganese, 4 oxygen and a calcium linked to a fourth manganese[2]. Oxidation of water leaves 2 H + on the lumenal side of the membrane, helping to establish the proton gradient essential for ATP synthesis in the CF1CF0-ATP sythase protein.   3D structures of photosystem II
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Additional ResourcesAdditional Resources
For additional information, see: Photosynthesis
ReferencesReferences
- ↑ Loll B, Kern J, Saenger W, Zouni A, Biesiadka J. Towards complete cofactor arrangement in the 3.0 A resolution structure of photosystem II. Nature. 2005 Dec 15;438(7070):1040-4. PMID:16355230 doi:http://dx.doi.org/10.1038/nature04224
- ↑ 2.0 2.1 Ferreira KN, Iverson TM, Maghlaoui K, Barber J, Iwata S. Architecture of the photosynthetic oxygen-evolving center. Science. 2004 Mar 19;303(5665):1831-8. Epub 2004 Feb 5. PMID:14764885 doi:http://dx.doi.org/10.1126/science.1093087