p hotophosphorylation chapter 19 19.6 abasıyanık 1
TRANSCRIPT
General Features H2Oelectron donor (NADH in
oxid.phosph) light good electron acceptor and donor similarity with OP; electron
carryingproton pumpingelectrochemical potential ATP synthasis
in chloroplast
Photosynthesis in 2 process in plants
1. light depending reactions (light reactions): plant illumated
2. 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 membraneslike mt inner membrane enclose thylakoids thylakoids:flattened 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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LİGHT ABSORPTİON
visible light400-700 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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photonhits to a chromophore’s electron (absorbing molecule’s) higher energy level (all or nothin event) excited state to ground state as light, or heat or chemical workexcited state
ground state
•light (fluoresenceemit lower frequence)•heat•chemical work transfer of energy to anotherexcition transfer
deca
y
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CHLOROPHYLL ABSORB LİGHT ENERGY
most import. pigment on thylakoidchlorophyll
chlorophyllgreen pigment with polycyclic, planar resembling protoporyphrin of hemoglobin with Mg2+
phytol side chain heterocyclic 5 ring aroung Mgextended polyene
structureabsorption of light two type: a and b
~twice a than b in plants chlorophyles with LHC
light-harveting complexes 7 a, 5 b, 2 accessorypigment (lutein)
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BACTERİ PHYCOBİLİNS
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cynobacterai & red algeaphycobilins phycoerythrobilin phycocyanoblin
extended polyene system but no Mg
covalently linked to protein phycobilinproteins associate in highly ordered complexes called
phycobilisomes primary light-harvesting structure
ACCESSORY PIGMENTS IN PLANTS
second light absorbing pigments called accessory pigments called carotenoids.
carotens: yellow, red or pruple -carotenemost important one
red-orange isoprenoid lutein (yellow carotenoids)
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THE CENTRAL PHOTOCHEMİCAL EVENT:LİGHT-DRİVEN ELECTRON FLOW 1952, Louis Duysen, Rhodospirillum rubrum,
870 nm lightbleached Kok and With680-700 nm nonbioloigc electron acceptor (no
illumination)bleaching electron lossbleaching pigments called P870, P680, P700
photosynthetic bacteria with simple phototransduction machinerytype 1: electron pheophytin (chlorophyll without Mg) a quinone
type 2: electrona quinone an iron-sulfur centerPlants and cyanobacteria have 2 photosystems (PSI- PSII) in tandem
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TYPE II REACTİON CENTER: PHEOPHYTİN-QUİNONE REACTİON CENTER
like complex III in mt
example:Rhodobacter viridisa large protein complex wth 4 PPC + 13 cofactors:2 pairs chlorophyll, a pair pheophytin, 2 quinones, nonheme iron, 4 heme with c-type cytocrome
cyclic
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TYPE I REACTİON CENTER: FE-S REACTİON CENTER
like complex III in mt
like Type I Reaction center
DIFFERENCE
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IN PLANTS:TWO REACTİON SYSTEM İN 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 a=b P680ecytochrome b6f proton movement
Photosytem I (PSI): like green-sulfur bacteria a>b P700eFe-S protein ferrodoxinNADP 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 O221