ch19b oksidatif fosforilasyon ve fotofosforilasyon yonca duman

8/3/2019 Ch19b Oksidatif Fosforilasyon Ve Fotofosforilasyon Yonca Duman

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PHOTOSYNTHETIC PHOSPHORYLATION

andPHOTOSYNTHESIS

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FOTOSENTEZ

Işık Reaksiyonları Karbon asimilasyon

reaksiyonları

Fotosentetik hücrelerin klorofil ATP ve NADPH; CO2 in

ve diğer pigmentleri ışık enerji- indirgenip trioz fosfatlar,sini absorblayarak ATP ve nişasta, glukoz, sükroza

NADPH şeklinde muhafaza indirgenmesinde kullanı-

ederler, aynı anda O2 oluşur. lır. Bu reaksiyonlar ışıkta

da, karanlıkta da olur.

O2

2

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Photosynthetic pigments, enzyme complexes of

ligth reactions and ATP synthase

Enzymes of carbon assimilation

reactions

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Reagent)(HillacceptorelectronArtificial:A

OAH2A2OH2

:ReactionHill

22Light

2 + → +

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:tschloroplasinReactionHill

2g

2 O2HNADPH2NADP2OH2 ++→+

++

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A molecule that has ab-sorbed a photon is in anexcited state, which isgenerally unstable. An

electron lifted into a hig-

her-energy orbital usu-ally returns rapidly to itsnormal lower-energy or-

bital ; the excited mole-cule decays to the stab-

le ground state, giving

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When isolated chlorophyll molecules in vitro are excited by light, the absorbed energy is

quickly released as fluorescence and heat .

up the absorbed quan-tum as light or heat orusing it to do chemi-cal work. Light emissi-

on accompanying de-cay of excited molecu-les (called fluorescen-ce) is always at a lon-ger wavelength (lowerenergy) than that of the

absorbed light.



When chlorophyll in intact leaves is

excited by visible light, the excited an-tenna chlorophyll transfers energy di-

rectly to a neighboring chlorophyll mo-lecule, which becomes excited as the

first molecule returns to its groundstate. This transfer of energy, exciton

transfer or resonance transfer .

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In this excited chlorophyll molecule, an

electron is promoted to a higher energy

orbital. This electron then passes to anearby electron acceptor that is part ofthe electron-transfer .



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Light Harvesting Complex (LHC II)

The functional unit isan LHC trimer, with36 chlorophyll and 6lutein molecules.Shown here is a

monomer, viewed inthe plane of themembrane, with itsthree

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ransmem rane α αα α -

helical segments ,seven chlorophyll a molecules (green),five chlorophyll b molecules (red), and

two molecules of the accessory pigment

lutein (yellow), whichform an internal cross-brace.



The functional unit isan LHC trimer, with36 chlorophyll and 6lutein molecules.Shown here is a

monomer, viewed inthe plane of themembrane, with itsthree transmembrane

Light Harvesting Complex (LHC II)

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α αα α - e ca segmen s ,

seven chlorophyll a molecules (light green), five chlorophyll b molecules (dark green), and two

molecules of the accessory pigment

lutein (yellow), whichform an internal cross-brace.



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Phycoerythrobilins and phycocyanobilins (phycobilin pigments) are thepigments of light harvesting complexes found in cyanobacteria and red

algae.

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A phycobilisome. The phycobilin pigments bound to specific proteins form complexes

called phycoerythrin (PE), phycocyanin (PC), and allophycocyanin (AP). The energy of

photons absorbed by PE or PC is conveyed through AP (a phycocyanobilin-binding

protein) to chlorophyll a of the reaction center by exciton transfer.

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When chlorophyll in intact leaves is

excited by visible light, the excited

antenna chlorophyll transfers energy

directly to a neighboring chlorophyllmolecule, which becomes excited as

the first molecule returns to itsground state. This transfer of energy,

exciton transfer .

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In this excited chlorophyll molecule,

an electron is promoted to a higherenergy orbital. This electron then

passes to a nearby electron acceptorthat is part of the electron-transfer .



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orexcitontransfer



Exciton and electrontransfer

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Type II Reaction Center Type I Reaction Center



46c) Cyanobacteria and higher plants



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( ) ( )2 2

Chl + 1 exiton Chl (excitation)∗

→



( ) ( ) ( )

( )

2 2

+B B 2

Chl + Pheo Chl + Pheo (charge separation)

2 Pheo + 2 H + Q 2 Pheo + Q H

∗ •+ •−

•−

→

→

1 ps = 10-12s

1 ns = 10-9 s

µs = - s

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( ) ( ) o2 2

+ o

2

(1) Chl Chl + e E -1.0 V

(2) Q + 2 H + 2 e QH E -0.045 V

∗ •+ −

−

′→ ≈

′→ ≈

o

o

E 0.045 V ( 1.0 V) 0.95 V

G 2 (96.5 kJ / V mol) 0.95 V 180 kJ / mol

′∆ = − − − ≈

′∆ = − ⋅ ⋅ ⋅ = −

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2 22 H O 2 NADP 8 Photons O 2 NADPH 2 H+ +

+ + → + +

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The overall reaction initiated by light in PSII:+ +

B B 24 P680 + 4 H + 2 PQ + 4 Photons 4 P680 + 2 PQ H→

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+ + +

red ox2 Fd + 2 H + NADP 2 Fd + NADPH + H→



Photosystem II of the cyanobacterium Synechococcus elongates

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The supramolecular complex of PSI and its associated antenna chlorophyllsFX , FA , FB : Fe-S proteinleri ; QK: Phylloquinone (A1)

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The functional homology

between the

cyanobacterial

cytochrome b6f

complex

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mitochondrialcytochrome

bc1complex,

and between

cyanobacterialcytochrome C6

and plant

plastocyanin.



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2 H2O→

4 H

+

+ O2 + 4 e

-

4 P680+

+ 4 Tyr→ 4 Tyr•+ 4 P680

4 Tyr•+ [Mn Complex]

0 → 4 Tyr + [Mn Complex]

+4

[Mn Complex]+4

+ 2 H2O→ [Mn Complex]0

+ 4 H+

+ O2

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The overall reaction initiated by light in PSII:+ +

B B 24 P680 + 4 H + 2 PQ + 4 Photons 4 P680 + 2 PQ H→



2 H2O→ 4 H+

+ O2 + 4 e-

4 P680+

+ 4 Tyr → 4 Tyr•

+ 4 P6804 Tyr

•+ [Mn Complex]

0 → 4 Tyr + [Mn Complex]

+4

[Mn Complex]+4

+ 2 H2O→ [Mn Complex]0

+ 4 H+

+ O2

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PSII ve Oksijen Oluşturan Kompleks’te proton pompalanması ve

elektron transferine ilişkin reaksiyonlar:

4 P680 + 4 H+ + 2PQB + 4 Foton → 4 P680+ + 2 PQBH2

4 P680+ + 4 Tyr → 4 P680 + 4 Tyr˙

4 Tyr˙ + [Mn kompleks]0→ 4 Tyr + [Mn kompleks]

+4

[Mn kompleks]+4 + 2 H2O → [Mn kompleks]0 + 4 H+ + O2

2 H2O + 2 PQB + 4 Foton → O2 + 2 PQBH2

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IşıklandırılankloroplastlardaherH + başına

protongradientindedepolananenerji



∆G=RTln∆pH+ZF∆ψ =-17kJ/mol

The overall equation for noncyclic photophosphorylation

2 H2O + 8 Photons + 2 NADP+

+ ≈ 3 ADP + ≈ 3Pi → O2 + ≈ 3 ATP + 2 NADPH + 2 H+

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ch19b oksidatif fosforilasyon ve fotofosforilasyon yonca duman

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