Transcript

PHOTOPHOSPHORYLATİONchapter 1919.6

Abasıyanık

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PHOTOSYNTHESİS: HARVESTİNG LİGHT ENERGY

vascular plants and algae

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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 ELECTRON FLOW İN CHLOPLAST

Ochoa showed that NADPH is acceptor

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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

Z scheme

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