Fluorescence parameters and redox kinetics allow measurement of PSII (and PSI) activities

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2 Fluorescence parameters and redox kinetics allow measurement of PSII (and PSI) activities

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4 Photosynthetic bacteria are divided into - anoxygenic - oxygenic and - Halobacteria

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8 One and two electron transporters: O A and Q B

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10 Photosystem II functions a dimer

11 Features of PSII - largest pigment/protein complex billion yrs old: very little modificaition during evolution -O 2 evolution: water-splitting apparatus -P 680 chlorophyll - D1/D2 dimer resembles L and M protein of bacterial photosystem - 24 proteins, several are nuclear-encoded: gene transfer (example: PsbO = 33 KDa protein) - plastid-encoded proteins: RNA editing - function of individual proteins - antisense, RNA i -kolines - plastid gene inactivation - homologs in Synechocystis

12 Features of PSII - D1 and D2 diversified during evolution: cf. Tyr-161 (Yz) - one/two electron transfers: Q A and Q B -Q B is herbicide-binding site - light sensitivity: photoinhibition - complex biosynthesis: stroma/grana transfer - D1 as an example for protein biosynthesis

13 D1

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15 D1 Protein - Hohes turnover - Neusynthese in Stromathylakoide - Cofaktorbindung - Faltung - translational arrest - Transport zu Granathylakoiden - Assoziation mit Antennenkomplexe -Fehlleitung der Elektronen: Destruktion (Photoinhibition) - D1/D2: 2 ähnliche Proteine mit unterschiedlichen Funktionen

16 D2: Homologes Protein Mit Unterschiedlicher Funktion

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18 Cyt b-559

19 The Mn cluster splits water and is responsible for O 2 evolution

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22 The Mn cluster sits at the lumenal site of PSII and is attached to the D1/D2 dimer

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24 Äußere Antennen

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26 Inner antenna proteins bind chlorophyll

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30 Photoinhibition

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33 Cytochrom b 6 /f-complex

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36 2 Hämgruppen vom b- Typ (Cytochrom b) 1 Hämgruppe vom c-typ (Cytochrom f)

37 Cytochrom b 6 /f-komplex Chinon/Semichinon/Hydrochinon b-typ Cytochrom: Cytochrom b c-typ Cytochrom: Cytochrom f Cyclischer Elektronentransport a) QH 2 Cytb Cytb QH b) Elektronen vom PSI Cytochromkomplex ist braun e - -Carrier in der Thylakoidmembran (Plastocyanin: löslich im Lumen) H + -Pumpe ph über Thylakoidmembran

38 Cytochrom b 6 /f-komplex Häm-Transport Laterale Heterogenität Plastoquinon-Pool Redox Signale Rieske Protein Laterale Heterogenität: Wanderung zwischen Grama (PSII) and Stroma (PSI) Valenzwechsel von Fe 2+ /Fe 3+ Cyclischer Elektronentransport vom PSI: Keine O2- and NADPH-Produktion, aber Verstärkung des Protonengradienten

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40 Photosystem I - receive 1 electron from plastocyanin (Cu, lumen) - docking sites: PsaF and PsaN - PsaA/PsaB heterodimer (twice as big as D1/D2) binds chl, a few car -P 700 -FeS X (electron acceptor) - PsaC (at stroma site) binds -FeS A and FeS B (electron acceptors) - transfers electron to ferredoxin - Ferredoxin (reversible attachment to PSI) - Ferredoxin-NADP + -Oxidoreductase - PSI contains 3 Fe 4 -S 4 clusters (biosynthesis?) - Plastids contain also Fe 2 -S 2 clusters

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46 Cyclic electron transport - electrons from PSI to cytochrome-b 6 f-complex, back to P no oxygen evolution, NADPH synthesis - generation of proton gradient

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49 Jagendorf and Uribe demonstrated that establishment of an electrochemical gradient across the membrane could lead to ATP synthesis. They equilibrated isolated chloroplasts for 60 seconds in a ph 4, adjusted the ph to 8 in the presence of ADP and Pi, and allowed phosphorylation to proceed for 15 seconds. The entire experiment was carried out in the dark.

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53 Mitochondrial ATPases are almost identical to plastid ATP synthase

54 Paul D. Boyer and John E. Walker have shown how the enzyme ATP synthase makes ATP. ATP synthase is found in chloroplast and mitochondrial membranes and in the cytoplasmic membrane of bacteria. A difference in hydrogen ion concentration across the membrane drives the enzyme to synthesise ATP. "The Binding Change Mechanism" Using chemical methods Paul Boyer proposed that ATP synthase is like a cylinder with alternating alpha and beta subunits. An asymmetricalgammasubunitin themiddleof thecylindercauseschangesin thestructureof thebetasubunitswhenitrotates(100 r.p.s.). He termed these structures open (beta O ), loose (beta L ) and tight (beta T ). Four stages in ATP synthesis

55 A molecular machine is discovered John Walker crystallised the enzyme to study its details. He established that Boyer's proposal for how ATP synthesis takes place, the "molecular machine", was correct. ATP synthase Theenzymeconsistsof an F O part bound in the membrane and a projecting F 1 part. The F 1 part is known in detail, while less is known about the F O part. The F O part consists of three different protein molecules (subunits a, b and c). When hydrogen ions flow through the membrane via a disc of c subunits, the disc is compelled to rotate. The gamma subunit in the F 1 part is fixed to the disc and therefore rotates with it. The alpha and beta subunits in the F 1 part, however, cannot rotate because they are locked in a fixed position by the b subunit, which is anchored to subunit a in the membrane. As the gamma subunit functions as an assymmetrical axle, the beta subunits are compelled to undergo the structural changes described in the figures above.

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64 Calvin Cyclus

65 Ribulose-1,5-bisphosphat-Carboxylase

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70 Photorespiration

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72 C4 photosynthesis

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77 Mesophyll cell Bundle sheet cell

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