P HOTOPHOSPHORYLATION chapter 19 19.6 Abasıyanık 1.
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P HOTOPHOSPHORYLATION chapter 19 19.6 Abasyank 1 Slide 2 P HOTOSYNTHESIS : HARVESTING LIGHT ENERGY vascular plants and algae 2 Slide 3 General Features H 2 O 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 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) 3 Slide 4 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 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. 4 Slide 5 LIGHT ELECTRON FLOW IN CHLOPLAST Ochoa showed that NADPH is acceptor 5 Slide 6 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 6 Slide 7 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 ground state light (fluoresence emit lower frequence) heat chemical work transfer of energy to another excition transfer decay 7 Slide 8 C HLOROPHYLL ABSORB LIGHT ENERGY most import. pigment on thylakoid chlorophyll chlorophyll green pigment with polycyclic, planar resembling protoporyphrin of hemoglobin with Mg 2+ 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) 8 Slide 9 BACTERI PHYCOBILINS 9 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 Slide 10 A CCESSORY P GMENTS N P LANTS second light absorbing pigments called accessory pigments called carotenoids. carotens: yellow, red or pruple -carotene most important one red-orange isoprenoid lutein (yellow carotenoids) 10 Slide 11 11 Slide 12 12 Slide 13 13 Slide 14 14 Slide 15 15 Slide 16 T HE C ENTRAL P HOTOCHEMICAL E VENT :L IGHT -D RIVEN E LECTRON F LOW 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 16 Slide 17 17 Slide 18 T YPE II REACTION CENTER : P HEOPHYTIN - QUINONE R EACTION C ENTER like complex III in mt example:Rhodobacter viridis a 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 18 Slide 19 T YPE I REACTION CENTER : F E -S R EACTION CENTER like complex III in mt like Type I Reaction center DIFFERENCE 19 Slide 20 20 Slide 21 I N P LANTS :T WO R EACTION SYSTEM IN T ANDEM 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 P680 e cytochrome b 6 f proton movement Photosytem I (PSI): like green-sulfur bacteria a>b 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 O 2 21 Slide 22 Z scheme 22 Slide 23 23 Slide 24 24 Slide 25 25 Slide 26 26 Slide 27 27 Slide 28 28 Slide 29 29 Slide 30 30 Slide 31 31 Slide 32 32 Slide 33 33 Slide 34 34 Slide 35 35