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P HOTOPHOSPHORYLATION chapter 19 19.6 Abasıyanık 1.

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Presentation on theme: "P HOTOPHOSPHORYLATION chapter 19 19.6 Abasıyanık 1."— Presentation transcript:

1 P HOTOPHOSPHORYLATION chapter Abasıyanık 1

2 P HOTOSYNTHESIS : HARVESTING LIGHT ENERGY vascular plants and algae 2

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

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

5 LIGHT  ELECTRON FLOW IN CHLOPLAST Ochoa showed that NADPH is acceptor 5

6 LIGHT ABSORPTION visible light  nm (violent-red) photon  a quantum of light energy is higher at 400 than 700 Why? frequency is higher at 400 6

7 photon  hits 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 work excited state ground state light (fluoresence  emit lower frequence) heat chemical work  transfer of energy to another  excition transfer decay 7

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

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

10 A CCESSORY P ıGMENTS ıN 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

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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  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

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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

19 T YPE I REACTION CENTER : F E -S R EACTION CENTER like complex III in mt like Type I Reaction center DIFFERENCE 19

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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

22 Z scheme 22

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