9/10/2012 1 Lecture 2: LIGHT Lecture 2: LIGHT REACTION REACTION 9/10/2012 9/10/2012 1 62 Slides COMPETENCIES COMPETENCIES Upon mastering the materials of this lecture, Upon mastering the materials of this lecture, students would be able to explain students would be able to explain 1. 1. The characteristics of light as a source of The characteristics of light as a source of energy in the process of photosynthesis energy in the process of photosynthesis 2. 2. The process of NADPH formation in the The process of NADPH formation in the conversion of radiation energy to be chemical conversion of radiation energy to be chemical energy energy 3. 3. The process of ATP formation in the conversion The process of ATP formation in the conversion of radiation energy to be chemical energy of radiation energy to be chemical energy 9/10/2012 9/10/2012 2 LECTURE OUTLINE LECTURE OUTLINE 9/10/2012 9/10/2012 3 What is photosynthesis? What is photosynthesis? The process of converting The process of converting solar energy solar energy into into chemical energy chemical energy. The process of CO The process of CO 2 reduction into reduction into carbohydrates (sugars) at the expense of carbohydrates (sugars) at the expense of NADPH & ATP NADPH & ATP Responsible for removal of ~ Responsible for removal of ~ 200 200 billion billion tons of C from the atmosphere yearly. tons of C from the atmosphere yearly. 9/10/2012 9/10/2012 4
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 of The 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 the The process of NADPH formation in the
conversion of radiation energy to be chemical conversion of radiation energy to be chemical energyenergy
3.3. The process of ATP formation in the conversion The process of ATP formation in the conversion of radiation energy to be chemical energyof radiation energy to be chemical energy
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LECTURE OUTLINELECTURE OUTLINE
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What is photosynthesis?What is photosynthesis? The process of converting The process of converting solar energy solar energy
into into chemical energychemical energy.. The process of COThe process of CO22 reduction into reduction into
carbohydrates (sugars) at the expense ofcarbohydrates (sugars) at the expense ofNADPH & ATPNADPH & ATP
Responsible for removal of ~ Responsible for removal of ~ 200 200 billion billion tons 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
Primaryelectronacceptor
Primaryelectronacceptor
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 for life on earth
Solar energy is created at the core of the sun Solar energy is created at the core of the sun when hydrogen atoms are fused into helium by when hydrogen atoms are fused into helium by nuclear fusion .nuclear fusion .
Temperatures of the sun are Temperatures of the sun are about about 15,000,00015,000,00000K K at the core, at the core,
and and about about 5,8005,80000K K at the photosphere at the photosphere
((radiativeradiative surface 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 of electromagnetic radiationelectromagnetic radiation Radiation is the transfer of energy through some
material or through space in the form of electromagnetic waves
Electromagnetic waves are the self-propagating, mutual oscillation of electric and magnetic fields. Electromagnetic waves move electromagnetic energy through space (either empty or filled with transparent matter)
Most of the electromagnetic radiation emitted Most of the electromagnetic radiation emitted from the sun's surface lies in the visible band from the sun's surface lies in the visible band centered at 500 nmcentered at 500 nm
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The Electromagnetic SpectrumThe Electromagnetic Spectrum
Shortest wavelengths(Most energetic photons)
Longest wavelengths(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 4.6 billion yearsbillion years and has enough fuel to go on for and has enough fuel to go on for another another five billion years five billion years or so. or so.
At the end of its life, the Sun will start to fuse At the end of its life, the Sun will start to fuse helium into heavier elements and begin to swell helium into heavier elements and begin to swell up, ultimately growing so large that up, ultimately growing so large that it will it will swallow the Earthswallow the Earth. .
After a billion years as a red giant, it will After a billion years as a red giant, it will suddenly collapse into a white dwarf suddenly collapse into a white dwarf ---- the final the final end product of a star like ours. It may take a end product of a star like ours. It may take a trillion 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 per unit area of the surface of a black body is unit area of the surface of a black body is directly proportional to the fourth power of directly proportional to the fourth power of its absolute temperature. That isits absolute temperature. That is
Apply StefanApply Stefan--Boltzmann Law To Sun and EarthBoltzmann Law To Sun and EarthR=R=TT44
Sun (Sun (6000 6000 00KK))RRSS = (5.67 x 10= (5.67 x 10--88 W/mW/m22 KK44) * (5800 ) * (5800 00K)K)44
= 64,164,532 W/m= 64,164,532 W/m22
Earth (3Earth (300 00 00KK))RREE = (5.67 x 10= (5.67 x 10--88 W/mW/m22 KK44) * (300) * (300 00K)K)44
= 459 W/m= 459 W/m22
Sun emits about 160,000 times more radiation Sun emits about 160,000 times more radiation per unit area than the Earth because Sun’s per unit area than the Earth because Sun’s temperature is about 20 times higher than temperature is about 20 times higher than Earth’s temperatureEarth’s temperature 600/300 = 20600/300 = 20
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Inverse Square LawInverse Square LawThe amount of radiation passing through a specific area is The amount of radiation passing through a specific area is inversely proportional to the square of the distance of that inversely proportional to the square of the distance of that area from the energy source. area from the energy source. I = E(I = E(44RR22)/()/(44rr22))I = Irradiance at the surface of I = Irradiance at the surface of
the outer spherethe outer sphereE = Irradiance at the surface of E = Irradiance at the surface of
the object (Sun)the object (Sun)R = 6.96 x 10R = 6.96 x 105 5 km (Radius of the Sun)km (Radius of the Sun)r r = 1.5 x 10= 1.5 x 108 8 kmkm (Average Sun(Average Sun--Earth Distance)Earth Distance)I = I = 64,164,532 W/mW/m2 2 x(6.96 x 10x(6.96 x 105 5 ))2 2 /(1.5 x 10/(1.5 x 108 8 ))22
I = 1382 W/mI = 1382 W/m2 2 (The generally accepted solar constant of 1368 W/m2 is a satellite measured yearly average)
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Radiation emitted by a human bodyRadiation emitted by a human body The net power radiated is the difference between The net power radiated is the difference between
the power emitted and the power absorbed:the power emitted and the power absorbed:Pnet = Pemit − Pabsorb.
Applying the StefanApplying the Stefan––Boltzmann law,Boltzmann law,R = (T4-T0
4)A = the total surface area of an adult is about A = the total surface area of an adult is about 2 m²2 m², , = t= the midhe mid-- and farand far--infrared infrared emissivityemissivity of skin and of skin and most most
clothing is near unity, as it is for most nonmetallic clothing is near unity, as it is for most nonmetallic surfaces. surfaces.
T = skin temperature is about T = skin temperature is about 3333°°CC, but clothing reduces , but clothing reduces the surface temperature to about the surface temperature to about 28 28 °°CC when the when the ambient temperature is ambient temperature is 20 20 °°CC. .
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Hence, the net radiative heat loss is about Pemit =0.97* 5.67×10−8 W m−2 K−4 *2 m2(273+28)4
= 902.92 W.m-2 or J.s-1
Pabsorbed = 0.97* 5.67×10−8 W m−2 K−4 *2 m2(273+27)4
= 890.98 W.m-2 or J.s-1
Pnet = 902.92-890.98 = 11.94 J.s-1
11.94 x 24 hours x 60 minutes x 60 seconds = 1,031,556.8 J/day
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Why are plants green?
Transmitted light
WHYWHY AREAREPLAPLANTS NTS GREGREEN? EN?
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2.2 Light2.2 Light
Light is an electromagnetic waveLight is an electromagnetic wave What is the electromagnetic wave? What is the electromagnetic wave? It is electricity and magnetism moving through the It is electricity and magnetism moving through the
spacespace
Light was known to Light was known to be a wavebe a wave
After producing After producing electromagnetic electromagnetic waves of other waves of other frequencies, it was frequencies, it was known to be an known to be an electromagnetic wave electromagnetic wave as well.as well.
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LIGHT AS A WAVE LIGHT AS A WAVE Wavelength (Wavelength (ll) ) –– the distance between crests (or the distance between crests (or
troughs) of a wavetroughs) of a wave Frequency (Frequency (vv)) –– the number of crests (or troughs) that the number of crests (or troughs) that
pass by each second.pass by each second. Speed (Speed (cc)) –– the rate at which a crest (or trough) moves the rate at which a crest (or trough) moves
((33..101055 km/s).km/s).Crest
Trough
l• Maxwell calculated the speed of
propagation of electromagnetic waves and found:
This is the speed of light in a vacuum.99//1010//20122012 1818
2.3 Quantum Theory2.3 Quantum TheoryLight as particles Light as particles •• Light comes in quanta of energy called Light comes in quanta of energy called photons photons –– little little
bulletsbullets of energy.of energy.•• A photon is a quantum or irreducible quantity of A 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 explain several physical phenomena observed in beginning of the 20th century light until further heating, then it will glow red, yellow then
"white" hot. It also did not explain colors given off by various elements as
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Planck's TheoryPlanck's Theory Energy cannot be absorbed or emitted Energy cannot be absorbed or emitted
unless it is a complete packet. unless it is a complete packet. Planck's theory states that atoms can Planck's theory states that atoms can
only absorb or release energy in fixed only absorb or release energy in fixed quantum unitsquantum units
• The amounts of energy an object emits or absorbs are called quantum (quanta plural)
• Related the Frequency of the radiation to the amount of energy.
E = hν = hc/lFrequency (v) = c/h = 6.6262 x 10-34 J-s (joule-seconds)c = speed of light (3x108 [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 terletak pada batas panjang gelombang 400 - 700 nm
• Radiasi pada batas panjang gelombang 400 - 700 nm disebut PAR (photosynthetically active radiation) atau cahaya nampak (visible radiation)
where where A A is Avogadro's number (= 6.02 x 10is Avogadro's number (= 6.02 x 102323 photons/mol)photons/mol)h h is Planck's constant (= 6.62 x 10is Planck's constant (= 6.62 x 10 --3434J s per photon)J s per photon)c c is the speed of light (= 3 x 10is the speed of light (= 3 x 1088 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.s a mol of blue light (l = 400 nm) = 298893.0 J.sa mol of blue light (l = 400 nm) = 298893.0 J.s a 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
10.55010.3.10.62.610.02.6
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Summary of PhotonsSummary of Photons
To describe interactions of light with matter, one To describe interactions of light with matter, one generally has to appeal to the particle (quantum) generally has to appeal to the particle (quantum) description of lightdescription of light
A single photon has an energy given by A single photon has an energy given by E = E = hhcc//ll
where where h = Planck’s constant = 6.6x10h = Planck’s constant = 6.6x10--3434 [J s] [J s] c c = speed of light = 3x10= speed of light = 3x1088 [m/s][m/s]l l = wavelength of the light (in [m])= wavelength of the light (in [m])
Photons also carry momentum. The momentum is Photons also carry momentum. The momentum is related to the energy by:related to the energy by:
p = E/p = E/cc = h/= h/ll
Photons can be treated as Photons can be treated as ““packets of lightpackets of light” which behave ” which behave as a particle.as a particle.
l
Representation of a Photon
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The reduction of CO2 to be carbohydrate through photosynthesis requires energy (NADPH & ATP)
Photosynthesis can be divided into two reactions Light Reaction Generation of NADPH2 Generation of ATP
Dark Reaction Diffusion of CO2 Reduction of CO2 C3, C4 & CAM
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 autotrophic Photosynthesis is the process by which autotrophic organisms use light energy to make sugar and organisms use light energy to make sugar and oxygen gas from carbon dioxide and water oxygen gas from carbon dioxide and water
This is an over simplification approach as HThis is an over simplification approach as H22O never O never meets COmeets CO22 directly in the photosynthesisdirectly in the photosynthesis
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ChloroplastsChloroplasts In most plants, photosynthesis occurs primarily in In most plants, photosynthesis occurs primarily in
the leaves, in the chloroplaststhe leaves, in the chloroplasts•• The leaves have the most chloroplastsThe 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 energyThe pigments absorb light energy
A chloroplast contains: A chloroplast contains: StromaStroma (a fluid)(a fluid) GranaGrana (stacks of (stacks of thylakoidsthylakoids) )
The The thylakoidsthylakoids contain contain chlorophyllchlorophyll Chlorophyll is the green pigment Chlorophyll is the green pigment
that captures light for that captures light for photosynthesisphotosynthesis9/10/20129/10/2012 3030
The location and structure of chloroplastsThe location and structure of chloroplasts
LEAF CROSS SECTION MESOPHYLL CELL
LEAF
Chloroplast
Mesophyll
CHLOROPLAST Intermembrane space
Outermembrane
Innermembrane
ThylakoidcompartmentThylakoidStroma
Granum
StromaGrana9/10/20129/10/2012 3131
1. Light Absorption2. Electron Exitation
Fluorescence Phosphorescence.
3. Electron Transfer4. NADPH Synthesis
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LIGHT ABSORBTION AND TRANSFERTO THE REACTION CENTERS
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LIGHT ABSORBTION AND TRANSFERTO THE REACTION CENTERS
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Resonance Energy Transfer Resonance 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 molecule Associated with the Associated with the thylakoidthylakoid
membranesmembranes ChlorophyllChlorophyll ChlChl a and a and ChlChl b (b (ChlChl c in some algae)c in some algae)
• Chl a has a methyl group (CH3)• Chl b has a carbonyl group (CHO)
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Phytol
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AbsorpsiAbsorpsi fotonfoton mengakibatkanmengakibatkan pengaturanpengaturanelektronelektron intramolekulintramolekul padapada pusatpusat reaksireaksi yang yang diikutidiikuti dengandengan tranfertranfer elektronelektron antarantar molekulmolekul
Pada mulanya, elektron khlorofil pada pusat reaksi tereksitasi pada orbit yang menjauhi inti atom dan molekul denganabsorpsi foton langsung atau lebih mungkin melalui transfer energi foton dari antena pigmen
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Water-splittingphotosystem
NADPH-producingphotosystem
ATPmill
Two types of Two types of photosystemsphotosystemscooperate in the cooperate in the light reactionslight reactions
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DuaDua orbit orbit dipertimbangkandipertimbangkan sebagaisebagaitempattempat eksitasieksitasi elektronelektron yaituyaitu orbit I orbit I dandanII (II (eksitasieksitasi I & II)I & II)
ElektronElektron yang yang tereksitasitereksitasi tidaktidak terikatterikatkuatkuat padapada molekulmolekul khlorofilkhlorofil dandan mudahmudahditransferditransfer keke molekulmolekul lain lain disekitarnyadisekitarnya. .
PusatPusat reaksireaksi yang yang tereksitasitereksitasi adalahadalahreduktorreduktor yang yang kuatkuat, , dandan bahkanbahkan cukupcukupkuatkuat untukuntuk mereduksimereduksi molekulmolekul lain yang lain yang tidaktidak siapsiap menerimamenerima elektronelektron. .
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Partial energy diagram for a photoluminescent system.9/10/20129/10/2012 4545 99//1010//20122012 4646
Red light absorbed by Red light absorbed by photosystemphotosystem II II (PSII) produces a (PSII) produces a strong oxidant strong oxidant and a and a weak weak reductantreductant. .
FarFar--redred light absorbed by light absorbed by photosystemphotosystem I I (PSI) produces a (PSI) produces a weak oxidant weak oxidant and a and a strong strong reductantreductant. .
The strong oxidant generated by PSII The strong oxidant generated by PSII oxidizes wateroxidizes water, while , while the strong the strong reductantreductant produced by PSI reduces produced by PSI reduces NADPNADP. .
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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 chlorophyll in a chloroplast
Loss of energy due to heat causes the photons of light to be less energetic.
Less energy translates into longer wavelength.
Energy = (Planck’s constant) x (velocity of light)/(wavelength of light)
Transition toward the red end of the visible spectrum.
NoncyclicNoncyclic PhotophosphorylationPhotophosphorylation PhotosystemPhotosystem II regains electrons by splitting water, leaving II regains electrons by splitting water, leaving
OO22 gas as a bygas as a by--productproduct
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The OThe O22 liberated by photosynthesis is made liberated by photosynthesis is made from the oxygen in water (Hfrom the oxygen in water (H++ and eand e--))
Plants produce OPlants produce O22 gas by splitting Hgas by splitting H22OO
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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. Z is a tyrosine Z is a tyrosine side chain on the reaction side chain on the reaction center protein D1. Electrons are extracted center protein D1. Electrons are extracted from water (Hfrom water (H22O) by the O) by the oxygenoxygen--evolvingevolvingcomplex and complex and rereducerereduce ZZ++. .
2.2. On the oxidizing side of PSII (to the left of On the oxidizing side of PSII (to the left of the arrow joining P680 with P680*), P680the arrow joining P680 with P680*), P680++
is is rereducedrereduced by Z, the immediate donor to by Z, the immediate donor to PSII.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 of On the reducing side of PSII (to the right of the arrow joining P680 with P680*), the the arrow joining P680 with P680*), the pheophytinpheophytin transfers electrons to the transfers electrons to the plastoquinoneplastoquinone acceptors Qacceptors QAA and Qand QBB. . 99//1010//20122012 5656
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5.5. The The cytochromecytochrome b.b.--ff complex transfers complex transfers electrons to electrons to plastocyaninplastocyanin (PC), which in turn (PC), which in turn reduces P700reduces P700++. .
6.6. The The b,b,--ff complex contains a complex contains a RieskeRieske ironiron--sulfursulfurprotein (protein (FeSRFeSR), two ), two bb--typetype cytochromescytochromes ((cytcytb), and b), and cytochromecytochrome f f ((cytcyt f). f).
7.7. The acceptor of electrons from P700* (AThe acceptor of electrons from P700* (A00) is ) is thought to be a chlorophyll, and the next thought to be a chlorophyll, and the next acceptor (Aacceptor (A11) may be a ) may be a quinonequinone. .
8.8. A series of A series of membranemembrane--boundbound ironiron--sulfursulfurproteins (proteins (FeSxFeSx, , FeSFeSBB, and , and FeSFeSAA) transfer ) transfer electrons to soluble electrons to soluble ferredoxinferredoxin ((FdFd). ).
9.9. The The flavoproteinflavoprotein ferredoxinferredoxin--NADPNADP reductasereductase((FpFp) serves to reduce NADP, which is used in ) serves to reduce NADP, which is used in the Calvin cycle to reduce COthe Calvin cycle to reduce CO22. .
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10.10. The dashed line indicates cyclic electron flow around The dashed line indicates cyclic electron flow around PSI. PSI.
11.11. PSII produces electrons that reduce the PSII produces electrons that reduce the cytochromecytochromeb.b.--ff complex, while PSI produces an oxidant that complex, while PSI produces an oxidant that oxidizes the oxidizes the cytochromecytochrome b.b.--ff complex. complex. P680 and P700 refer to the wavelengths of maximum P680 and P700 refer to the wavelengths of maximum absorption of the reaction center chlorophylls in PSII absorption of the reaction center chlorophylls in PSII and PSI and PSI
12.12. The electron of PSI is then excited upon absorption of The electron of PSI is then excited upon absorption of radiation energy and transfer to Aradiation energy and transfer to A00 (chlorophyll)(chlorophyll)
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13.13. The transfer of electron occurs from AThe transfer of electron occurs from A00to A1 (to A1 (quinonequinone), ), FeSxFeSx, , FeSFeSBB, & , & FeSFeSAA((membranemembrane--boundbound ironiron--sulfursulfur proteinsproteins), ), FdFd ((soluble soluble ferredoxinferredoxin ), ), FpFp((flavoproteinflavoprotein ferredoxinferredoxin--NADPNADPreductasereductase) and finally to NADP) and finally to NADP++
14.14. It was found antagonistic effects of light It was found antagonistic effects of light on on cytochromecytochrome oxidation.oxidation.
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HH22O O Z (PSII)Z (PSII)PP680680* * (PSII reaction center (PSII reaction center chlorophyll) chlorophyll) PheoPheo ((pheophytinpheophytin))QQAA and and QQB B ((plastoquinoneplastoquinone acceptors)acceptors)CytochromeCytochromeb.b.--ff complex complex PCPC ((plastocyaninplastocyanin))PP700700+ +
3.3. BerapaBerapa NADPH NADPH dihasildihasil daridari hasilhasil fotolisisfotolisis air ?air ?4.4. Tingkat Tingkat CahayaCahaya didi Malang Malang sekitarsekitar 1 mmol.s1 mmol.s--11, ,
berapaberapa NADPH yang NADPH yang dihasilkandihasilkan dengandengan tingkattingkatcahayacahaya demikiandemikian ? ?
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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 in What is the function of water in
photosynthesis ? photosynthesis ? 3.3. What is the event to happen after the light What is the event to happen after the light
interception by pigments interception by pigments 4.4. What is the first molecule receiving What is the first molecule receiving
electrons from the pigments (chlorophyll) electrons from the pigments (chlorophyll) excited at PS I excited at PS I
5.5. What is the first molecule receiving What is the first molecule receiving electrons from the pigments (chlorophyll) electrons from the pigments (chlorophyll) excited at PS IIexcited at PS II
