Photophosphorylation

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Photophosphorylation

• chapter 19
• 19.6
• Abasiyanik

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Photosynthesis harvesting light energy

• vascular plants and algae

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• General Features
• H2O?electron donor (NADH in oxid.phosph)
• light ? good electron acceptor and donor
• similarity with OP electron carrying?proton
  pumping?electrochemical potential ?ATP synthasis
• in chloroplast
• Photosynthesis in 2 process in plants
• light depending reactions (light reactions)
  plant illumated
• Carbon-assimilation reactions (carbon fixation or
  dark reactions) triose phosphates, starch,
  sucrose and others produced (in chapter 20)

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• Photosynthesis in CHLOROPLAST
• organelle found in plants and algea
• they have a third membrane system
• both light and dark reaction here
• a few micrometer in dia.
• two membranes?like mt
• inner membrane enclose thylakoids
• thylakoidsflattened vesicles (membrane)
• all pigments,
• electron-transport complexes
• ATP synthese
• grana thylakoid stack
• Adjacent grana are connected by non-stacked
  membranes called stroma lamellae
• The fluid around thylakoids ? stroma
• space inside thylakoids ? lumen.

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light ? electron flow in chloplast

• Ochoa showed that NADPH is acceptor

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light absorption

• visible light?400-700 nm (violent-red)
• photon? a quantum of light
• energy is higher at 400 than 700
• Why? frequency is higher at 400

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• photon?hits to a chromophores electron
  (absorbing molecules) ?higher energy level (all
  or nothin event) ?excited state ?to ground state
• as light, or heat or chemical work

excited state

• light (fluoresence?emit lower frequence)
• heat
• chemical work ?transfer of energy to
  another?excition transfer

decay
ground state
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Chlorophyll absorb light energy

• most import. pigment on thylakoid?chlorophyll
• chlorophyll?green pigment with polycyclic, planar
  resembling protoporyphrin of hemoglobin with Mg2
• phytol side chain
• heterocyclic 5 ring aroung Mg?extended polyene
  structure?absorption of light
• two type a and b
• twice a than b in plants
• chlorophyles with LHC
• light-harveting complexes
• 7 a, 5 b, 2 accessory
• pigment (lutein)

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bacteri ?phycobilins

• cynobacterai red algea?phycobilins
• phycoerythrobilin
• phycocyanoblin
• extended polyene system but no Mg
• covalently linked to protein phycobilinproteins
• associate in highly ordered complexes called
  phycobilisomes
• primary light-harvesting structure

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Accessory Pigments in Plants

• second light absorbing pigments called accessory
  pigments called carotenoids.
• carotens yellow, red or pruple
• ?-carotene?most important one
• red-orange isoprenoid
• lutein (yellow carotenoids)

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The Central Photochemical EventLight-Driven
Electron Flow

• 1952, Louis Duysen, Rhodospirillum rubrum, 870 nm
  light?bleached
• Kok and With?680-700 nm
• nonbioloigc electron acceptor (no
  illumination)?bleaching
• electron loss?bleaching
• pigments called ?P870, P680, P700

photosynthetic bacteria with simple
phototransduction machinery type 1 electron
?pheophytin (chlorophyll without Mg) ? a
quinone type 2 electron?a quinone ? an
iron-sulfur center Plants and cyanobacteria have
2 photosystems (PSI- PSII) in tandem
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Type II reaction center Pheophytin-quinone
Reaction Center
exampleRhodobacter viridis?a large protein
complex wth 4 PPC 13 cofactors2 pairs
chlorophyll, a pair pheophytin, 2 quinones,
nonheme iron, 4 heme with c-type
cytocrome cyclic
like complex III in mt
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Type I reaction center Fe-S Reaction center
like Type I Reaction center DIFFERENCE
like complex III in mt
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In PlantsTwo Reaction system in Tandem

• In which organisms ?
• vascular plants
• Algea
• cyanobacteria
• Two different kinds of photosystems
• Photosytem II (PSII) pheophytin-quinone type of
  system (like purple bacteria) with Chloropyll a
  b
• ab
• P680?e?cytochrome b6f ?proton movement
• Photosytem I (PSI) like green-sulfur bacteria
• agtb
• P700?e?Fe-S protein ferrodoxin?NADP ?NAPH
• plants PSI PSII works tandem to carry electron
  form water to NADP
• plastocyanin connects PSII to PSI
• protein
• like cytochrome c in mt
• oxygenic photosynthesis water ?NADPH and O2

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Z scheme
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