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LECTURE 3:NADPH AND ATP

SYNTHESIS

LECTURE OUTCOMEStudents, after mastering the materials of the present lecture, should be able to:1. To explain the conversion mechanism of light energy to

chemical energy (NADPH & ATP)2. To explain electron excitation and flow in the

conversion mechanism of light energy to chemical energy

3. To explain the relationship between light energy and wave length

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LECTURE OUTLINE

Fluorescence Phosphorescence

LIGHT ABSORBTION LIGHT ABSORBTION LIGHT ABSORBTION LIGHT ABSORBTION

AND TRANSFERAND TRANSFERAND TRANSFERAND TRANSFER

TO THE REACTION TO THE REACTION TO THE REACTION TO THE REACTION

CENTERSCENTERSCENTERSCENTERS

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Resonance Energy Transfer - Radiationless

e- e-

e-

e-

e-

e-

e-

e-

hv

Ground state

Excited state

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1. Absorpsi foton mengakibatkan pengaturanelektron intramolekul pada pusat reaksi yang diikuti dengan tranfer elektron antar molekul

2. Pada mulanya, elektronkhlorofil pada pusat reaksitereksitasi pada orbit yang menjauhi inti atom dan molekul dengan

absorpsi foton langsungatau lebih mungkinmelalui transfer energifoton dari antena pigmen

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Excited

ATPmill

� Two types of photosystems (PS) cooperate in the light reactions

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Water-splittingphotosystem

NADPH-producingphotosystem

PS IIPS IIPS IIPS II PS IPS IPS IPS I

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� Fluorescence� Emisi cahaya dari molekul yang sedang diiradiasi

sebagai akibat dari penurunan elektron dari orbait 1 ke orbit dasar. Proses ini tidak tergantung suhu danberlangsung cepat (lifetime <10-8 detik). Panjanggelombang lebih besar dari panjang gelombangyang diabsorpsi (chlorophyll a mengabsorpsi cahayapada 430 & 630 nm, dan mengemisi cahaya pada668 nm).

� Phosphorescence� Emisi cahaya dari molekul sebagai akibat penurunan

elektron dari “triplet state” ke orbit dasar. Cahayayang dihasilkan berlangsung relatif perlahan (10-4 –2 detik), dan panjang gelombang relatif sangatpanjang

Excited statee−−−−

HeatLight

Photon

Light(fluorescence)

Chlorophyllmolecule

Groundstate

2

Absorption of a photon

Excitation of chlorophyll in a chloroplast

Fluorescence of tonic water (Left),

and an acetone solution of

chlorophyll under direct UV

irradiation (Right).

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3. Red light absorbed by photosystem II (PSII) produces a strong oxidant and a weak reductant.

4. Far-red light absorbed by photosystem I (PSI) produces a weak oxidant and a strong reductant.

5. The strong oxidant generated by PSII oxidizes water, while the strong reductant produced by PSI reduces NADP.

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1.1.1.1. HHHH2222OOOO

2.2.2.2. Z (PSII)Z (PSII)Z (PSII)Z (PSII)

3.3.3.3. PPPP680680680680* (PSII reaction * (PSII reaction * (PSII reaction * (PSII reaction center chlorophyll)center chlorophyll)center chlorophyll)center chlorophyll)

4.4.4.4. PheoPheoPheoPheo ((((pheophytinpheophytinpheophytinpheophytin))))

5.5.5.5. QQQQAAAA and Qand Qand Qand QB B B B

((((plastoquinoneplastoquinoneplastoquinoneplastoquinoneacceptors)acceptors)acceptors)acceptors)

6.6.6.6. CytochromeCytochromeCytochromeCytochrome b.b.b.b.----ffffcomplex complex complex complex

7.7.7.7. PCPCPCPC ((((plastocyaninplastocyaninplastocyaninplastocyanin))))

8.8.8.8. P700P700P700P700+ + + + ((((PSI reaction PSI reaction PSI reaction PSI reaction center chlorophyll)center chlorophyll)center chlorophyll)center chlorophyll)

9.9.9.9. AAAA0000 (chlorophyll ?)(chlorophyll ?)(chlorophyll ?)(chlorophyll ?)

10.10.10.10. AAAA1111 ((((quinonequinonequinonequinone?)?)?)?)

11.11.11.11. FeSxFeSxFeSxFeSx, , , , FeSFeSFeSFeSBBBB, & , & , & , & FeSFeSFeSFeSAAAA

((((membranemembranemembranemembrane----boundboundboundboundironironironiron----sulfursulfursulfursulfur proteinsproteinsproteinsproteins))))

12.12.12.12. FdFdFdFd ((((soluble soluble soluble soluble ferredoxinferredoxinferredoxinferredoxin))))

13.13.13.13. FpFpFpFp ((((flavoproteinflavoproteinflavoproteinflavoproteinferredoxinferredoxinferredoxinferredoxin----NADPNADPNADPNADPreductasereductasereductasereductase))))

14.14.14.14. NADPNADPNADPNADP

Primaryelectron acceptor

Primaryelectron acceptor

Photons

PHOTOSYSTEM I

PHOTOSYSTEM II

Energy forsynthesis of

by chemiosmosis

Noncyclic Photophosphorylation� Photosystem II regains electrons by splitting water, leaving

O2 gas as a by-product

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� The O2 liberated by photosynthesis is made from the oxygen in water (H+ and e-)

Plants produce O2 gas by splitting H2O

The red X indicates that protons do not directly pass through the cytochrome complex.

Protons cross the membrane via oxidation and reduction of quinones

X

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1.1.1.1. Z is a tyrosineZ is a tyrosineZ is a tyrosineZ is a tyrosine side chain on the reaction center protein D1. Electrons are extracted from water (H2O) by the oxygenthe oxygenthe oxygenthe oxygen----evolving evolving evolving evolving complexcomplexcomplexcomplex (OECOECOECOEC)and rereduce Z+.

2. On the oxidizing side of PSII (to the left of the arrow joining P680 with P680*), P680+

is rereduced by Z, the immediate donor to PSII.

https://en.wikipedia.org/wiki/File:Photosystem-II_2AXT.PNG

3. The excited PSII reaction center chlorophyll, (P680*) transfers an electron to pheophytin(Pheo).

4. On the reducing side of PSII (to the right of the arrow joining P680 with P680*), the pheophytin transfers electrons to the plastoquinone acceptors QA and QB.

5. The cytochrome b.-f complex transfers electrons to plastocyanin (PC), which in turn reduces P700+.

6. The b,-f complex contains a Rieske iron-sulfur protein (FeSR), two b-type cytochromes (cytb), and cytochrome f (cyt f).

7. The acceptor of electrons from P700* (A0) is thought to be a chlorophyll, and the next acceptor (A1) may be a quinone.

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8. A series of membrane-bound iron-sulfur proteins (FeSx, FeSB, and FeSA) transfer electrons to soluble ferredoxin (Fd).

9. The flavoprotein ferredoxin-NADP reductase(Fp) serves to reduce NADP, which is used in the Calvin cycle to reduce CO2.

10. The dashed line indicates cyclic electron flow around PSI.

11. PSII produces electrons that reduce the cytochrome b.-f complex, while PSI produces an oxidant that oxidizes the cytochrome b.-f complex.

P680 and P700 refer to the wavelengths of maximum absorption of the reaction center chlorophylls in PSII and PSI

12. The electron of PSI is then excited upon

absorption of radiation energy and transfer to

A0 (chlorophyll)

13. The transfer of electron occurs from A0 to A1

(quinone), FeSx, FeSB, & FeSA

(membrane-bound iron-sulfur proteins), Fd

(soluble ferredoxin ), Fp (flavoprotein

ferredoxin-NADP reductase) and finally to

NADP+

14. It was found antagonistic effects of light on

cytochrome oxidation.

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HHHH2222O O O O →→→→Z (PSII)Z (PSII)Z (PSII)Z (PSII)→→→→P680P680P680P680* * * * (PSII reaction center (PSII reaction center (PSII reaction center (PSII reaction center

chlorophyll) chlorophyll) chlorophyll) chlorophyll) →→→→PheoPheoPheoPheo ((((pheophytinpheophytinpheophytinpheophytin))))→→→→QQQQAAAA and and and and

QQQQB B B B ((((plastoquinoneplastoquinoneplastoquinoneplastoquinone acceptors)acceptors)acceptors)acceptors)→→→→CytochromeCytochromeCytochromeCytochrome

b.b.b.b.----ffff complex complex complex complex →→→→PCPCPCPC ((((plastocyaninplastocyaninplastocyaninplastocyanin))))→→→→P700P700P700P700+ + + +

(PSI reaction center chlorophyll) (PSI reaction center chlorophyll) (PSI reaction center chlorophyll) (PSI reaction center chlorophyll) →→→→AAAA0000

(chlorophyll ?)(chlorophyll ?)(chlorophyll ?)(chlorophyll ?)→→→→AAAA1111 ((((quinonequinonequinonequinone?) ?) ?) ?) →→→→FeSxFeSxFeSxFeSx, , , ,

FeSFeSFeSFeSBBBB, & , & , & , & FeSFeSFeSFeSAAAA ((((membranemembranemembranemembrane----boundboundboundbound ironironironiron----sulfursulfursulfursulfur

proteinsproteinsproteinsproteins) ) ) ) →→→→ FdFdFdFd ((((soluble soluble soluble soluble ferredoxinferredoxinferredoxinferredoxin ))))→→→→FpFpFpFp

((((flavoproteinflavoproteinflavoproteinflavoprotein ferredoxinferredoxinferredoxinferredoxin----NADPNADPNADPNADP

reductasereductasereductasereductase))))→→→→NADPNADPNADPNADP

1.1.1.1. EksitasiEksitasiEksitasiEksitasi 1 1 1 1 mol e mol e mol e mol e padapadapadapada setiapsetiapsetiapsetiap pusatpusatpusatpusat reaksireaksireaksireaksi (PSII & (PSII & (PSII & (PSII &

PSI) PSI) PSI) PSI) membutuhkanmembutuhkanmembutuhkanmembutuhkan 1 1 1 1 kuantakuantakuantakuanta cahayacahayacahayacahaya. . . . ReduksiReduksiReduksiReduksi 1 1 1 1

mol NADP mol NADP mol NADP mol NADP →→→→ 1 1 1 1 mol mol mol mol NADPH NADPH NADPH NADPH membutuhkanmembutuhkanmembutuhkanmembutuhkan 2 2 2 2 mol mol mol mol

eeee

2.2.2.2. BerapaBerapaBerapaBerapa kuantakuantakuantakuanta cahayacahayacahayacahaya dibutuhkandibutuhkandibutuhkandibutuhkan untukuntukuntukuntuk

pembentukanpembentukanpembentukanpembentukan 1 1 1 1 mol NADPH ?mol NADPH ?mol NADPH ?mol NADPH ?

3.3.3.3. BerapaBerapaBerapaBerapa NADPH NADPH NADPH NADPH dihasildihasildihasildihasil daridaridaridari hasilhasilhasilhasil fotolisisfotolisisfotolisisfotolisis air ?air ?air ?air ?

4.4.4.4. Tingkat Tingkat Tingkat Tingkat CahayaCahayaCahayaCahaya didididi Malang Malang Malang Malang sekitarsekitarsekitarsekitar 1 1 1 1 mmol.smmol.smmol.smmol.s----1111, , , ,

berapaberapaberapaberapa NADPH yang NADPH yang NADPH yang NADPH yang dihasilkandihasilkandihasilkandihasilkan dengandengandengandengan tingkattingkattingkattingkat

cahayacahayacahayacahaya demikiandemikiandemikiandemikian ? ? ? ?

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1.1.1.1. Where does the light reaction happen ?Where does the light reaction happen ?Where does the light reaction happen ?Where does the light reaction happen ?

2.2.2.2. What is the function of water in What is the function of water in What is the function of water in What is the function of water in photosynthesis ? photosynthesis ? photosynthesis ? photosynthesis ?

3.3.3.3. What is the event to happen after the light What is the event to happen after the light What is the event to happen after the light What is the event to happen after the light interception by pigments interception by pigments interception by pigments interception by pigments

4.4.4.4. What is the first molecule receiving What is the first molecule receiving What is the first molecule receiving What is the first molecule receiving electrons from the pigments (chlorophyll) electrons from the pigments (chlorophyll) electrons from the pigments (chlorophyll) electrons from the pigments (chlorophyll) excited at PS I excited at PS I excited at PS I excited at PS I

5.5.5.5. What is the first molecule receiving What is the first molecule receiving What is the first molecule receiving What is the first molecule receiving electrons from the pigments (chlorophyll) electrons from the pigments (chlorophyll) electrons from the pigments (chlorophyll) electrons from the pigments (chlorophyll) excited at PS IIexcited at PS IIexcited at PS IIexcited at PS II

Compiled crystal structure of chloroplast F1F0 ATP synthase

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� A portion of the photon’s energy is captured as the high-energy phosphate bond in ATP

� Electron flow must occur for the formation of ATP (photophosphorylation), although under some conditions electron flow may not be accompanied by phosphorylation.

� It is now widely accepted that photophosphorylation works via the chemiosmotic mechanism, first proposed in the 1960s by Peter Mitchell

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1. The basic principle of chemiosmosis is that ion concentration differences and electrical potential differences across membranes are Chemiosmosise energy that can be utilized by the cell.

2. As described by the second law of thermodynamics, any nonuniform distribution of matter or energy represents a source of energy.

3. Chemical potential differences of any molecular species whose concentrations are not the same on opposite sides of a membrane provide such a source of energy.

4. Proton flow from one side of the membrane to the other accompanies electron flow in addition to the asymmetric nature of the photosynthetic membrane

5. The direction of proton translocation is such that

the STROMA BECAMES MORE ALKALINE and the

LUMEN BECAMES MORE ACIDIC when electron

transport occurs.

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� The synthesis of ATP in chloroplasts occurs when the energy of a proton gradient is coupled to phosphorylateADP to ATP by an F-type ATPase

� Protons are accumulated on the inside of the thylakoidlumen and depleted in the stroma compartment

pH of chloroplast compartmentThylakoid lumen Stroma

Dark 7.0 7.0

Light 5.2 8.2

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� Some of the early evidence in support of a chemiosmotic mechanism.

� Andre Jagendorf and co-workers suspended chloroplasts in a pH 4 buffer, which permeated the membrane and caused the interior, as well as the exterior, of the thylakoid to equilibrate at this acidic pH. They then rapidly injected the suspension into a pH 8 buffer solution thereby creating a pH difference of 4 units across the thylakoid membrane , with the inside acidic relative to the outside.

� They found that large amounts of ATP were formed from ADP and Pi by this process, without any light input or electron transport.

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� The ATP is synthesized by a large (400-kDa) enzyme complex known as the coupling factor, ATPase, ATP synthase or CF0-CF1.

� This enzyme consists of two parts: a hydrophobic membrane bound portion called CF0 and a portion that sticks out into the stromacalled CF1.

� CF0 appears to be a channel across the membrane through which protons can pass, while CF1 is the portion of the complex that actually synthesizes ATP.

Subunit composition of chloroplast F1F0 ATP synthase. This enzyme consists of a large multisubunit complex, CF1 and CF0. CF1consists of five different polypepticles, with stoichiometry of α3, β3, γ, ε.

CF0 contains probably four different polypeptides, with a stoichiometry of a, b, b', C14. Protons from the lumen are transported by the rotating c polypepticle and ejected on the stroma side. (Figure courtesy of W. Frasch in Taiz & Zeiger, 2010)

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� Total energy available for ATP synthesis, proton motive force (∆p), is the sum of a proton chemical potential and a transmembraneelectrical potential and

� These two components of the proton motive force from the outside of the membrane to the inside are given by

∆∆∆∆p = p = p = p = ∆∆∆∆EmEmEmEm –––– 59(59(59(59(pHpHpHpHiiii –––– pHpHpHpH0000) (mV)) (mV)) (mV)) (mV)

� ∆Em (or ∆ψ) is the transmenbrane potential

and pH1- pH0 (or ∆pH) is the pH difference

across the membrane.

� Total energy available for ATP synthesis, proton motive force (∆p), is the sum of a proton chemical potential and a transmembrane electrical potential and

� These two components of the proton motive force from the outside of the membrane to the inside are given by

∆∆∆∆p = p = p = p = ∆∆∆∆EmEmEmEm –––– 59(59(59(59(pHpHpHpHiiii –––– pHpHpHpH0000) (mV)) (mV)) (mV)) (mV)� ∆Em (or ∆ψ) is the transmenbrane potential and

pH1- pH0 (or ∆pH) is the pH difference across the

membrane.

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PHOTOSYSTEM I

H+ H+H+ H+H+ H+

H+ H+

H+ H+H+ H+H+ H+

H+ H+

H+ H+H+ H+H+ H+

H+ H+

H+ H+H+ H+H+ H+

H+ H+

H+ H+H+ H+H+ H+

H+ H+

H+ H+H+ H+H+ H+

H+ H+

H+ H+H+ H+H+ H+

H+ H+

H+ H+H+ H+H+ H+

H+ H+

H+ H+H+ H+H+ H+

H+ H+

H+ H+H+ H+H+ H+

H+ H+

H+ H+H+ H+H+ H+

H+ H+

H+ H+H+ H+H+ H+

H+ H+

H+ H+H+ H+H+ H+

H+ H+

H+ H+H+ H+H+ H+

H+ H+

H+ H+H+ H+H+ H+

H+ H+

H+ H+H+ H+H+ H+

H+ H+

H+ H+H+ H+H+ H+

H+ H+

H+ H+H+ H+H+ H+

H+ H+

H+ H+H+ H+H+ H+

H+ H+

H+ H+H+ H+H+ H+

H+ H+

H+ H+H+ H+H+ H+

H+ H+

H+ H+H+ H+H+ H+

H+ H+

H+ H+H+ H+H+ H+

H+ H+

H+ H+H+ H+H+ H+

H+ H+

H+ H+H+ H+H+ H+

H+ H+

H+ H+H+ H+H+ H+

H+ H+

H+

H+

H+

H+

H+

H+H+ H+

H+

H+ H+

H+

H+ADP+ Pi

ATP

4.67 H+

Thylakoid Lumen – compartment of low pH

Chloroplast stroma – region of high pH

PHOTOPHOSPHORYLATION

ATP Synthase(F-type ATPase)

� Based on the equation, a transmembrane

pH difference of one unit is equivalent to a

membrane potential of 59 mV.

� Under conditions of steady state electron

transport in chloroplasts, the membrane

electrical potential is quite small, so ∆p is

due almost entirely to ∆pH

� The stoichiometry of protons translocated

to ATP synthesis has been to be

(14/3)H+/ATP , before 3H+/ATP.

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� Herbicides are xenobiotics (foreign chemicals to

plants) that are designed to kill plants but are not

supposed to harm humans and animals.

� Ideally, herbicides will only kill weeds and various

noxious plants, leaving crops unharmed.

� Major types of herbicides

� Hormone mimics: e.g. 2,4-D mimics the plant

hormone auxin. (trade-name of Weed-B-Gone)

� Inhibitors of biosynthetic pathways unique to plants:

e.g. glyphosphate (Round-up)

� Inhibitors of photosynthetic electron transport: e.g.

methyl viologen (Paraquat) and atrazine

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� Process for ATP generation associated with some Photosynthetic Bacteria

• Electron in Photosystem I is excited and transferred to

ferredoxin that shuttles the electron to the cytochrome

complex.

• The electron then travels down the electron chain and

re-enters photosystem I

Cyclic photophosphorylation

� In sulfur bacteria, only one photosystem is used

� Generates ATP via electron transport� Anoxygenic photosynthesis� Excited electron passed to electron

transport chain� Generates a proton gradient for ATP

synthesis

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1. How many is H+ transported across membrane from lumen to stroma for the transfer of each 1e- to NADP+

2. How many is ATP produced for each formation of 1 NADPH

3. How much is the light quanta required for each formation of ATP

4. What does it mean by proton motive force

5. What is the enzyme catalyzing the synthesis of ATP from ADP

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