Lect2 Light Reaction 20121

8/10/2019 Lect2 Light Reaction 20121

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Lecture 2: LIGHTLecture 2: LIGHTREACTIONREACTION

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62 Slides

COMPETENCIESCOMPETENCIESUpon mastering the materials of this lecture,Upon mastering the materials of this lecture,students would be able to explainstudents would be able to explain1.1. The characteristics of light as a source ofThe characteristics of light as a source of

energy in the process of photosynthesisenergy in the process of photosynthesis2.2. The process of NADPH formation in theThe process of NADPH formation in the

conversion of radiation energy to be chemicalconversion of radiation energy to be chemicalenergyenergy

3.3. The process of ATP formation in the conversionThe process of ATP formation in the conversionof radiation energy to be chemical energyof radiation energy to be chemical energy

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LECTURE OUTLINELECTURE OUTLINE

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Wh at is ph otosynthesis? Wh at is ph otosynthesis?

The process of converting The process of converting solar energysolar energyintointo chemical energychemical energy ..

The process of CO The process of CO 22 reduction intoreduction intocarbohydrates (sugars) at the expense of carbohydrates (sugars) at the expense of NADPH & ATPNADPH & ATPResponsible for removal of ~Responsible for removal of ~ 200 200 billionbilliontons of C from the atmosphere yearly.tons of C from the atmosphere yearly.

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2 H + 1/2

Water-splittingphotosystem

Reaction-center

chlorophyll

Light

Primaryelectronacceptor

Energyto make



NADPH-producingphotosystem

Light

NADP

1

23

How the Light Reactions Generate NADPH and ATP

PS II

PS I

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Photosynthesis has two major phases :1. The absorbance of light and production of chemical forms of

energy (light reactions)2. The fixation and reduction of carbon and other oxidized

molecules (dark reactions)

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Solar energy is the ultimate source of energy forlife on earthSolar energy is created at the core of the sunSolar energy is created at the core of the sunwhen hydrogen atoms are fused into helium bywhen hydrogen atoms are fused into helium bynuclear fusion .nuclear fusion .

Temperatures of the sun are Temperatures of the sun areaboutabout 15,000,00015,000,000 00KK at the core,at the core,andandaboutabout 5,8005,800 00KK at the photosphereat the photosphere((radiativeradiativesurface of the sun)surface of the sun)

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The solar energy is then transmitted in the form of The solar energy is then transmitted in the form ofelectromagnetic radiationelectromagnetic radiation

Radiation is the transfer of energy through somematerial or through space in the form ofelectromagnetic wavesElectromagnetic waves are the self-propagating, mutualoscillation of electric and magnetic fields.Electromagnetic waves move electromagnetic energythrough space (either empty or fil led with transparentmatter)

Most of the electromagnetic radiation emittedMost of the electromagnetic radiation emitted

from the sun's surface lies in the visible bandfrom the sun's surface lies in the visible bandcentered at 500 nmcentered at 500 nm

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The Electromagnetic Spectrum The Electromagnetic Spectrum

Shortest wavelength(Most energetic photons)

Longest wavelength(Least energetic photons)

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The Sun appears to have been active for The Sun appears to have been active for 4.6 4.6billion yearsbillion yearsand has enough fuel to go on forand has enough fuel to go on foranotheranother five billion yearsfive billion years or so.or so.At the end of its life, the Sun will start to fuseAt the end of its life, the Sun will start to fusehelium into heavier elements and begin to swellhelium into heavier elements and begin to swellup, ultimately growing so large thatup, ultimately growing so large that it will it willswallow the Earthswallow the Earth. .After a billion years as a red giant, it willAfter a billion years as a red giant, it willsuddenly collapse into a white dwarfsuddenly collapse into a white dwarf -- -- the finalthe finalend product of a star like ours. It may take aend product of a star like ours. It may take atrillion years to cool off completely.trillion years to cool off completely.

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2.1 Stefan2.1 Stefan Boltzmann LawBoltzmann Law

This law states that the power emitted per This law states that the power emitted perunit area of the surface of a black body isunit area of the surface of a black body isdirectly proportional to the fourth power ofdirectly proportional to the fourth power ofits absolute temperature. That isits absolute temperature. That is

R=R= TT44

R = radiation flux (W.mR = radiation flux (W.m --22 = J.m= J.m --22.s.s --11))= emissivity (0= emissivity (0 1)1)

= Stefan= Stefan- -Boltzmann constant (5,67032 x 10Boltzmann constant (5,67032 x 10--88

W.mW.m--22

.K .K --44

)) T = absolute T = absolute temperturetemperture (273 +(273 + 00C).C).

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Apply StefanApply Stefan- -Boltzmann Law To Sun and EartBoltzmann Law To Sun and EartR=R= TT44

Sun (Sun ( 60006000 00K K ))RRSS = (5.67 x 10= (5.67 x 10 --88 W/mW/m 22 K K 44) * (5800) * (5800 00K)K)44

= 64,164,532 W/m= 64,164,532 W/m 22

Earth (3Earth (3 0000 00K K ))RREE = (5.67 x 10= (5.67 x 10 --88 W/mW/m 22 K K 44) * (300) * (300 00K)K)44

= 459 W/ m= 459 W/ m 22

Sun emits about 160,000 times more radiationSun emits about 160,000 times more radiationper unit area than the Earth because Sunsper unit area than the Earth because Suns

temperature is about 20 times higher thantemperature is about 20 times higher thanEarths temperatureEarths temperature 600/ 300 = 20600/ 300 = 20

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Inverse Square LawInverse Square Law The amount of radiation passing through a specific area is The amount of radiation passing through a specific area isinversely proportional to the square of the distance of thatinversely proportional to the square of the distance of thatarea from the energy source.area from the energy source.

I = E(I = E(44 RR22)/()/(44 r r 22))

I = Irradiance at the surface ofI = Irradiance at the surface ofthe outer spherethe outer sphere

E = Irradiance at the surface ofE = Irradiance at the surface ofthe object (Sun)the object (Sun)

R = 6.96 x 10R = 6.96 x 10 55 km (Radius of the Sun)km (Radius of the Sun)rr = 1.5 x 10= 1.5 x 10 88 kmkm(Average Sun(Average Sun- -Earth Distance)Earth Distance)I =I = 64,164,532 W/mW/m 22 x(6.96 x 10x(6.96 x 10 55 )) 22 / (1.5 x 10/ (1.5 x 10 88 )) 22

I = 1382 W/ mI = 1382 W/ m 22 (The generally accepted solar constant of1368 W/m 2 is a satelli te measured yearly average)

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Radiation emitted by a human bodRadiation emitted by a human bod The net power radiated is the difference between The net power radiated is the difference betweenthe power emitted and the power absorbed:the power emitted and the power absorbed:

P net = P emit P absorb .Applying the StefanApplying the Stefan Boltzmann law,Boltzmann law,

R = (T 4-T04)A = the total surface area of an adult is aboutA = the total surface area of an adult is about 2 m 2 m, ,

= t= t he midhe mid- - and farand far- -infraredinfrared emissivityemissivity of skin andof skin and mostmostclothing is near unity, as it is for most nonmetallicclothing is near unity, as it is for most nonmetallicsurfaces.surfaces.

T = skin temperature is about T = skin temperature is about 33 33CC, but clothing reduces, but clothing reducesthe surface temperature to aboutthe surface temperature to about 28 28 CCwhen thewhen theambient temperature isambient temperature is 20 20 CC..

T T 00 = the ambient temperature is about= the ambient temperature is about 25 25 00CCin Malangin Malang9/10/20129/10/2012 1414

Hence, the net radiative heat loss is aboutPemit =

0.97* 5.6710 8 W m 2 K 4 *2 m 2(273+28) 4= 902.92 W.m -2 or J.s -1

Pabsorbed =0.97* 5.6710 8 W m 2 K 4 *2 m 2(273+27) 4= 890.98 W.m -2 or J.s -1

P net = 902.92-890.98 = 11.94 J.s -111.94 x 24 hours x 60 minutes x 60 seconds =1,031,556.8 J/ day

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Why are plants g reen?

Transmitted light

WHYWHY AREAREPLAPLANTSNTS GREGREEN?EN?

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2.2 Light2.2 Light

Light is an electromagnetic waveLight is an electromagnetic waveWhat is t he electr omagnetic wave?What is t he electr omagnetic wave?It is electricity and magnetism moving through theIt is electricity and magnetism moving through thespacespace

Light was known toLight was known tobe a wavebe a waveAfter producingAfter producingelectromagneticelectromagneticwaves of otherwaves of otherfrequencies, it wasfrequencies, it wasknown to be anknown to be anelectromagnetic waveelectromagnetic wave

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LIGHT AS A WAVELIGHT AS A WAVEWavelength (Wavelength ( ll)) the distance between crests (orthe distance between crests (ortroughs) of a wavetroughs) of a waveFrequency (Frequency ( vv)) the number of crests (or troughs) thatthe number of crests (or troughs) thatpass by each second.pass by each second.Speed (Speed ( cc)) the rate at which a crest (or trough) movesthe rate at which a crest (or trough) moves((33..1010 55 km/ s).km/ s). Crest

Trough

l Maxwell calculated the speed of

propagation of electromagneticwaves and found:

This is the speed of light in a vacuum.99//1010//20122012 1818

2.3 Quantum Theory2.3 Quantum TheoryLight as particlesLight as particles Light comes in quanta of energy calledLight comes in quanta of energy called photons photons littlelittle

bulletsbulletsof energy.of energy. A photon is a quantum or irreducible quantity ofA photon is a quantum or irreducible quantity of

electromagnetic radiation.electromagnetic radiation. By the 1900's the wave model was accepted by scientist

as how light moved. Ideas of quantum theory were developed when

classical physics (the wave model) could not explainseveral physical phenomena observed in beginning of

the 20th centurylight until fur ther heating, then it w ill glow red, yellow th en"wh ite" hot.It also did not explai n colors given off by variou s elements asthey burn

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Planck's TheoryPlanck's TheoryEnergy cannot be absorbed or emittedEnergy cannot be absorbed or emittedunless it is a complete packet.unless it is a complete packet.Planck's theory states that atoms canPlanck's theory states that atoms canonly absorb or release energy in fixedonly absorb or release energy in fixedquantum unitsquantum units

The amounts of energy an object emits or absorbs arecalled quantum (quanta plural)

Related the Frequency of the radiation to the amount ofenergy.

E = h = hc/ l

Frequency (v) = c/h = 6.6262 x 10 -34 J-s (joule-seconds)c = speed of light (3x10 8 [m/ s)

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Visible radiation: visible to our eyes (wavelength:0.4x10 -6 - 0.7x10 -6 m)

Red = 0.65 mm, Orange = 0.60 mm, Yellow = 0.55 mm,Green = 0.50 mm, Blue = 0.45 mm & Violet = 0.40 mm

Cahaya dan PAR Tanaman dalam proses fotosintesis hanya dapat

memanfaatkan pancaran radiasi matahari yang terletakpada batas panjang gelombang 400 - 700 nm

Radiasi pada batas panjang gelombang 400 - 700 nmdisebut PAR (photosynthetically active radiation) ataucahaya nampak (visible radiation)

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DenganDenganmemasukkanmemasukkanhargaharga- -hargahargakonstantakonstanta, ,makamaka

dimanadimana dalamdalamsatuansatuannanonanometer (nm)meter (nm)SebagaiSebagai contohcontoh, , kandungankandunganenergienergi cahayacahayamerahmerah( ( = 680 nm)= 680 nm) adalahadalah

1 J (Joule) = 101 J (Joule) = 10 77 erg; 1 c (cal) = 4,2 J; 1erg; 1 c (cal) = 4,2 J; 1 eV eV= 1,6.10= 1,6.10 --1212 ergerg

JE

1710.878,19

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wherewhereAAis Avogadro's number (= 6.02 x 10is Avogadro's number (= 6.02 x 10 2323 photons/ mol)photons/ mol)hh is Planck's constant (= 6.62 x 10is Planck's constant (= 6.62 x 10 --3434 J s per photon) J s per photon)cc is the speed of light (= 3 x 10is the speed of light (= 3 x 10 88 m.sm.s --11).).

For instance,For instance,the energy of "green light" (= 550 nm) is:the energy of "green light" (= 550 nm) is:

E = 217376.7 J.sE = 217376.7 J.sa mol of blue light (l = 400 nm) = 298893.0 J.sa mol of blue light (l = 400 nm) = 298893.0 J.sa mol of red light (l = 700 nm) = 170796.0 J.sa mol of red light (l = 700 nm) = 170796.0 J.s

chAE

..

m

smcphotonsJhmolphotonsAE

9

83423

10.550

10.3.10.62.610.02.6

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Summary of PhotonsSummary of Photons

To describe interactions of light with matter, one To describe interactions of light with matter, onegenerally has to appeal to the particle (quantum)generally has to appeal to the particle (quantum)description of lightdescription of lightA single photon has an energy given byA single photon has an energy given by

E =E = hhc c // llwherewhereh = Plancks constant = 6.6x10h = Plancks constant = 6.6x10 --3434 [J s][J s]cc = speed of light = 3x10= speed of light = 3x10 88 [m/ s][m/ s]ll = wavelength of the light (in [m])= wavelength of the light (in [m])Photons also carry momentum. The momentum isPhotons also carry momentum. The momentum isrelated to the energy by:related to the energy by:

p = E/p = E/ c c = h/= h/ ll

Photons can be treated asPhotons can be treated aspackets of light packets of light which behave which behaveas a particle.as a particle.

l

Representation of a Photon

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The reduction of CO 2 to be carbohydratethrough photosynthesis requires energy(NADPH & ATP)Photosynthesis can be divided into tworeactions

Light ReactionGeneration of NADPH 2Generation of ATP

Dark ReactionDiffusion of CO 2Reduction of CO 2

C3, C4 & CAM

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Light ReactionLight Reaction1.1. Light AbsorptionLight Absorption2.2. PigmentsPigments3.3. Electron ExcitationElectron Excitation

FluorescenceFluorescencePhosphorescencePhosphorescence

4.4. Electron transfer & Synthesis NADPHElectron transfer & Synthesis NADPH5.5. Proton exchange & Synthesis ATPProton exchange & Synthesis ATP

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Photosynthesis is the process by which autotrophicPhotosynthesis is the process by which autotrophicorganisms use light energy to make sugar andorganisms use light energy to make sugar andoxygen gas from carbon dioxide and wateroxygen gas from carbon dioxide and water

This is an over simplification approach as H This is an over simplification approach as H 22O neverO nevermeets COmeets CO 22 directly in the photosynthesisdirectly in the photosynthesis

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ChloroplastsChloroplastsIn most plants, photosynthesis occurs primarily inIn most plants, photosynthesis occurs primarily inthe leaves, in the chloroplaststhe leaves, in the chloroplasts The leaves have the most chloroplasts The leaves have the most chloroplasts The green color comes from chlorophyll in the The green color comes from chlorophyll in the

chloroplastschloroplasts The pigments absorb light energy The pigments absorb light energy

A chloroplast contains:A chloroplast contains:StromaStroma(a fluid)(a fluid)GranaGrana(stacks of(stacks of thylakoidsthylakoids) )

The The thylakoidsthylakoidscontaincontainchlorophyllchlorophyll

Chlorophyll is the green pigmentChlorophyll is the green pigmentthat captures light forthat captures light for

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The location and structure of chloroplastsThe location and structure of chloroplasts

LEAF CROSS SECTION MESOPHYLL CELL

LEAF

Chloroplast

Mesophyll

CHLOROPLAST Intermembrane space

Outer membrane

Inner membrane

ThylakoidcompartmentThylakoid

Stroma

Granum

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1. Light Absorption2. Electron Exitation

Fluorescence

Phosphorescence.

3. Electron Transfer4. NADPH Synthesis

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LIGHT ABSORBTIONAND TRANSFERTO THE REACTIONCENTERS

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LIGHT ABSORBTIONAND TRANSFERTO THE REACTIONCENTERS

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Resonance Energy TransferResonance Energy Transfer -- RadiationlessRadiationless

e - e -

e -

e -

e -

e -

e -

e -

hv

Ground state

Excited state

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Pigment = a light absorbing moleculePigment = a light absorbing moleculeAssociated with theAssociated with the thylakoidthylakoidmembranesmembranesChlorophyllChlorophyll

ChlChl a anda and ChlChl b (b (ChlChl c in some algae)c in some algae)

XanthophyllsXanthophyllsCarotenoidsCarotenoids

--carotenecarotene

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Phytol tail

Porphyrin ring delocalized e-

Chl a has a methyl group (CH3) Chl b has a carbonyl group (CHO)

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Phytol

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AbsorpsiAbsorpsi fotonfotonmengakibatkanmengakibatkanpengaturanpengaturanelektronelektron intramolekulintramolekul padapadapusatpusat reaksireaksi yangyangdiikutidiikuti dengandengantranfertranferelektronelektron antarantarmolekulmolekul

Pada mulanya, elektronkhlorofil pada pusatreaksi tereksitasi padaorbit yang menjauhi intiatom dan molekul denganabsorpsi foton langsungatau lebih mungkinmelalui transfer energifoton dari antenapigmen

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Water-splittingphotosystem

NADPH-producingphotosystem

ATPmill

Two types of Two types ofphotosystemsphotosystemscooperate in thecooperate in thelight reactionslight reactions

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DuaDuaorbitorbit dipertimbangkandipertimbangkansebagaisebagaitempattempat eksitasieksitasi elektronelektronyaituyaitu orbit Iorbit I dandanII (II (eksitasieksitasi I & II)I & II)ElektronElektron yangyang tereksitasitereksitasi tidaktidak terikatterikatkuatkuatpadapadamolekulmolekul khlorofilkhlorofil dandan mudahmudahditransferditransfer ke kemolekulmolekul lainlain disekitarnyadisekitarnya. .PusatPusat reaksireaksi yangyang tereksitasitereksitasi adalahadalahreduktorreduktor yangyang kuatkuat, , dandan bahkanbahkancukupcukupkuatkuatuntukuntuk mereduksimereduksi molekulmolekul lain yanglain yangtidaktidak siapsiapmenerimamenerimaelektronelektron ..

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Partial energy diagram for a photoluminescent system.9/10/20129/10/2012 4545 99//1010//20122012 4646

FluorescencFluorescenc :: EmisiEmisi cahayacahayadaridari molekulmolekul yangyangsedangsedangdiiradiasidiiradiasisebagaisebagai akibatakibatdaridari penurunanpenurunanelektronelektron daridari orbaitorbait 1 1 kekeorbitorbit dasardasar. . ProsesProsesiniinitidaktidaktergantungtergantungsuhusuhu dandanberlangsungberlangsungcepatcepat(lifetime(lifetime 1010 --88 detikdetik).). PanjangPanjanggelombanggelombanglebihlebihbesarbesar daridari panjangpanjanggelombanggelombangyangyang diabsorpsidiabsorpsi(chlorophyll a(chlorophyll a mengabsorpsimengabsorpsi cahayacahayapadapada430 &430 &630 nm,630 nm, dandanmengemisimengemisi cahayacahayapadapada668 nm).668 nm).PhosphorescencePhosphorescence :: EmisiEmisi cahayacahayadaridari molekulmolekulsebagaisebagaiakibatakibatpenurunanpenurunan elektronelektrondaridari triplettripletstatestate kekeorbitorbit dasardasar. . CahayaCahayayangyang dihasilkandihasilkanberlangsungberlangsungrelatif relatif perlahanperlahan (10(10 --44 22 detikdetik),),dandanpanjangpanjanggelombanggelombangrelatif relatif sangatsangatpanjangpanjang

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Red light absorbed byRed light absorbed by photosystemphotosystemII II(PSII) produces a(PSII) produces a strong oxidantstrong oxidant and a and aweakweak reductantreductant. .FarFar--redredlight absorbed bylight absorbed by photosystemphotosystemI I(PSI) produces a(PSI) produces a weak oxidantweak oxidant and aand astrongstrong reductantreductant. .

The strong oxidant generated by PSII The strong oxidant generated by PSIIoxidizes wateroxidizes water, while, while the strongthe strongreductantreductant produced by PSI reducesproduced by PSI reducesNADPNADP..

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Excitedstate

e

HeatLight

Photon

Light(fluorescence)

Chlorophyllmolecule

Groundstate

2

(a) Absorption of a photon

(b) fluorescence of isolated chlorophyll in solution

Excitation of chlorophyllin a chloroplast

Loss of energy due to heatcauses the photons of light to beless energetic.

Less energy translates intolonger wavelength.

Energy = (Plancks constant) x(velocity of light)/(wavelength oflight)

Transition toward the red end ofthe visible spectrum.

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1.1. HH22OO2.2. Z (PSII)Z (PSII)3.3. PP680680* (PSII reaction* (PSII reaction

center chlorophyll)center chlorophyll)4.4. PheoPheo( (pheophytinpheophytin) )5.5. QQAA and Qand Q BB

((plastoquinoneplastoquinoneacceptors)acceptors)

6.6. CytochromeCytochrome b.b.- -f f

complexcomplex7.7. PCPC((plastocyaninplastocyanin) )

8.8. P700P700 ++ ((PSI reactionPSI reactioncenter chlorophyll)center chlorophyll)

9.9. AA00 (chlorophyll ?)(chlorophyll ?)10.10. AA11 ((quinonequinone?) ?)11.11. FeSxFeSx, , FeSFeS BB, &, & FeSFeS AA

((membranemembrane- -boundboundironiron- -sulfursulfurproteinsproteins) )

12.12. FdFd((solublesoluble ferredoxinferredoxin) )13.13. FpFp((flavoproteinflavoprotein

ferredoxinferredoxin- -NADPNADPreductasereductase) )14.14. NADPNADP

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Primaryelectron acceptor

Primaryelectron acceptor

Photons

PHOTOSYSTEM I

PHOTOSYSTEM II

Energy for synthesis of

by chemiosmosis

NoncyclicNoncyclicPhotophosphorylationPhotophosphorylationPhotosystemPhotosystemII regains electrons by splitting water, leavingII regains electrons by splitting water, leavingOO22 gas as a bygas as a by- -productproduct

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The OThe O 22 liberated by photosynthesis is madeliberated by photosynthesis is madefrom the oxygen in water (Hfrom the oxygen in water (H ++ and eand e --))

Plants produce OPlants produce O 22 gas by splitting Hgas by splitting H 22OO

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The red X indicates that protonsdo not directly pass throug h thecytochrome complex.

Protons cross the membrane viaoxidation and reduction of quinones

X

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1.1. Z is a tyrosineZ is a tyrosine side chain on the reactionside chain on the reactioncenter protein D1. Electrons are extractedcenter protein D1. Electrons are extractedfrom water (Hfrom water (H 22O) by theO) by the oxygenoxygen- -evolvingevolvingcomplex andcomplex and rereducerereduceZ Z++ ..

2.2. On the oxidizing side of PSII (to the left ofOn the oxidizing side of PSII (to the left ofthe arrow joining P680 with P680*), P680the arrow joining P680 with P680*), P680 ++isis rereducedrereducedby Z, the immediate donor toby Z, the immediate donor toPSII.PSII.

3.3. The excited PSII reaction center chlorophyll, The excited PSII reaction center chlorophyll,(P680*) transfers an electron to(P680*) transfers an electron to pheophytinpheophytin((PheoPheo).).

4.4. On the reducing side of PSII (to the right ofOn the reducing side of PSII (to the right ofthe arrow joining P680 with P680*), thethe arrow joining P680 with P680*), thepheophytinpheophytintransfers electrons to thetransfers electrons to theplastoquinoneplastoquinoneacceptorsacceptors AA and Qand Q BB..99//1010//20122012 5656


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5.5. The The cytochromecytochrome b.b.- -f f complex transferscomplex transferselectrons toelectrons to plastocyaninplastocyanin (PC), which in turn(PC), which in turnreduces P700reduces P700 ++ ..

6.6. The The b,b,- -f f complex contains acomplex contains a RieskeRieskeironiron--sulfursulfurprotein (protein (FeSRFeSR), two), two b b--typetypecytochromescytochromes( (cytcytb), andb), and cytochromecytochrome ff ((cytcyt f).f).

7.7. The acceptor of electrons from P700* (A The acceptor of electrons from P700* (A 00) is) isthought to be a chlorophyll, and the nextthought to be a chlorophyll, and the nextacceptor (Aacceptor (A 11) may be a) may be a quinonequinone. .

8.8. A series ofA series of membranemembrane- -boundboundironiron--sulfursulfurproteins (proteins (FeSxFeSx, , FeSFeS BB, and, and FeSFeS AA) transfer) transferelectrons to solubleelectrons to soluble ferredoxinferredoxin ( (FdFd).).

9.9. The The flavoproteinflavoprotein ferredoxinferredoxin- -NADPNADPreductasereductase((FpFp) serves to reduce NADP, which is used in) serves to reduce NADP, which is used inthe Calvin cycle to reduce COthe Calvin cycle to reduce CO 22..

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10.10. The dashed line indicates cyclic electron flow aroundThe dashed line indicates cyclic electron flow aroundPSI.PSI.

11.11. PSII produces electrons that reduce thePSII produces electrons that reduce the cytochromecytochromeb.b.- -f f complex, while PSI produces an oxidant thatcomplex, while PSI produces an oxidant thatoxidizes theoxidizes the cytochromecytochromeb.b.- -f f complex.complex.P680 and P700 refer to the wavelengths of maximumP680 and P700 refer to the wavelengths of maximumabsorption of the reaction center chlorophylls in PSIIabsorption of the reaction center chlorophylls in PSIIand PSIand PSI

12.12. The electron of PSI is then excited upon absorption ofThe electron of PSI is then excited upon absorption ofradiation energy and transfer to Aradiation energy and transfer to A00 (chlorophyll)(chlorophyll)

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13.13. The transfer of electron occurs from A The transfer of electron occurs from A 00to A1 (to A1 (quinonequinone), ), FeSxFeSx, , FeSFeS BB, &, & FeSFeS AA((membranemembrane- -boundboundironiron--sulfursulfur proteinsproteins), ),FdFd((solublesoluble ferredoxinferredoxin ), ), FpFp((flavoproteinflavoprotein ferredoxinferredoxin- -NADPNADPreductasereductase) and finally to NADP) and finally to NADP ++

14.14. It was found antagonistic effects of lightIt was found antagonistic effects of lightonon cytochromecytochromeoxidation.oxidation.

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HH22OO Z (PSII)Z (PSII) PP680680** (PSII reaction center(PSII reaction centerchlorophyll)chlorophyll) PheoPheo( (pheophytinpheophytin) ) QQAAandandQQBB((plastoquinoneplastoquinoneacceptors)acceptors) CytochromeCytochromeb.b.- -f f complexcomplex PCPC((plastocyaninplastocyanin) ) PP700700 ++(PSI reaction center chlorophyll)(PSI reaction center chlorophyll) AA00(chlorophyll ?)(chlorophyll ?) AA11 ((quinonequinone?) ?) FeSxFeSx, ,FeSFeS BB, &, & FeSFeS AA((membranemembrane- -boundboundironiron- -sulfursulfurproteinsproteins) ) FdFd((solublesoluble ferredoxinferredoxin) ) FpFp((flavoproteinflavoproteinferredoxinferredoxin- -NADPNADPreductasreducta s )) NADNAD

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1.1. EksitasiEksitasi1 mol e1 mol e padapadasetiapsetiappusatpusatreaksireaksi(PSII &(PSII &PSI)PSI) membutuhkanmembutuhkan1 1 kuantakuantacahayacahaya. . ReduksiReduksi1 1mol NADPmol NADP 1 mol1 mol NADPHNADPH membutuhkanmembutuhkan2 mol 2 molee

2.2. BerapaBerapakuantakuantacahayacahayadibutuhkandibutuhkanuntuk untuk pembentukanpembentukan1 mol NADPH ?1 mol NADPH ?

3.3. BerapaBerapaNADPHNADPH dihasildihasildaridarihasilhasil fotolisisfotolisisair ?air ?4.4. TingkatTingkat CahayaCahayadi diMalangMalang sekitarsekitar1 mmol.s1 mmol.s --11,,

berapaberapaNADPH yangNADPH yang dihasilkandihasilkandengandengantingkattingkatcahayacahayademikiandemikian? ?

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1.1. Where does the light reaction happen ?Where does the light reaction happen ?2.2. What is the function of water inWhat is the function of water in

photosynthesis ?photosynthesis ?3.3. What is the event to happen after the lightWhat is the event to happen after the light

interception by pigmentsinterception by pigments4.4. What is the first molecule receivingWhat is the first molecule receiving

electrons from the pigments (chlorophyll)electrons from the pigments (chlorophyll)excited at PS Iexcited at PS I

5.5. What is the first molecule receivingWhat is the first molecule receivingelectrons from the pigments (chlorophyll)electrons from the pigments (chlorophyll)

excited at PS IIexcited at PS II9/10/20129/10/2012 6262

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Lect2 Light Reaction 20121

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