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Photosynthesis The Source of most Biological Energy Trapped in Photosynthesis Energy Converted to Chemical Bonds Respiration: CH2O + O2 CO2 + H2O + ATP Krebs cycle CO2 ETS + Ox Phos O2 glycolysis sugar cytosol pyruvate mitochondrion NADH mitochondrion H2O matrix cristae ATP ATP Photosynthesis: CH2O + O2 CO2 + H2O + light sucrose Calvin cycle CO2 LR + P Phos O2 sugar synthesis triose chloroplast NADPH chloroplast H2O cytosol stroma thylakoid Light ATP Light: An Energy Waveform With Particle Properties Too wavelength violet blue green yellow orange red 400 500 600 700 nm wavelength (nm) 10-9 meter 0.000000001 meter! Light: An Energy Waveform With Particle Properties Too wavelength visible spectrum 400 500 600 700 nm wavelength (nm) 10-9 meter 0.000000001 meter! White light: all the colors humans can see at once QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. http://www.alanbauer.com/photogallery/Water/Rainbow%20over%20Case%20Inlet-Horz.jpg http://www.chez.com/uvinnovatio n/site/images/introduction/apple_l ogo.gif QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Which side of our brains are we using? QuickTime™ and a TIFF (Uncomp resse d) d eco mpres sor are nee ded to s ee this picture . http://jojoretrotoybox.homestead.com/files/Rainbow_Brite_Logo_2.jpg QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTime™ and a TIFF (Uncomp resse d) d eco mpres sor are nee ded to s ee this picture . QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. http://www.astrostreasureches t.net/websmurfclub/images/pin smurfoncloudrainbow.jpg http://www.tvtome.com/images/shows/4/8/40-11946.jpg http://www.coreywolfe.com/NOV%202004/mlp.jpg White Light Green is reflected! Leaf Pigments Absorb Most Colors Light: An Energy Waveform With Particle Properties Too amplitude brightness intensity Many metric units for different purposes We will use an easy-to-remember English unit: foot-candle 0 fc = darkness 100 fc = living room 1,000 fc = CT winter day 10,000 fc = June 21, noon, equator, 0 humidity Photosynthetic Rate What wavelengths of light drive photosynthesis? 100% 0 Action Spectrum green light reflected some still drives photosynthesis 400 visible spectrum 500 600 wavelength (nm) 700 nm Light beyond 700 nm has insufficient energy to drive photosynthesis Photosystem II chlorophyll b Light P450 lutein P470 to: ETS e- zeaxanthin P480 ß-carotene P500 In each energy transfer some energy is lost as heat: 2nd law of thermodynamics. from: H2O lycopene P510 echlorophyll b But enough energy is passed to P680 to eject an electron to the electron transport system. P650 chlorophyll a P680 Chlorophyll a Chlorophyll b CH2 CH2 HC H3C CH3 H N N Mg H N H3C HC C2H5 H3C H N H CH3 C2H5 N Mg H N H3C H N H H CH2 O=COCH O 3 O=C O H2C CH H3C C CH2 H2C CH2 H3C CH CH2 H2C CH2 H3C CH CH2 H2C CH2 HC H3C CH3 H2C CH3 H H CH2 O=COCH O 3 O=C O H2C CH H3C C CH2 H2C CH2 H3C CH CH2 H2C CH2 H3C CH CH2 H2C CH2 HC H3C CH3 Photosynthetic pigments are amphipathic CH3 CH3 CH3 CH3 CH HC C CH3 HC H3C H H2C Zeaxanthin HO CHO H N ß-Carotene CH HC C CH3 HC H3C CH HC C CH3 HC CH HC C CH3 HC CH HC CH H3C C CH HC CH H3C C CH HC CH3 H3C CH HC CH H3C C CH HC CH H3C C CH HC CH3 H3C H3C H3C OH Lutein 100% What intensities of light drive photosynthesis? Reaction Rate Photosynthesis add to reserve grow reproduce Respiration Using reserves and may die 0 0 10 100 compensation point 1,000 10,000 fc Light Intensity (fc) The example plant shown here “breaks even” at an intensity we have in our homes…a house plant! 100% What intensities of light drive photosynthesis? Reaction Rate Photosynthesis A 0 Photosynthesis B Respiration Shade tolerant plant dies in intense light! 0 10 100 compensation points 1,000 10,000 fc Light Intensity (fc) The second example plant shown here cannot survive in our homes…it is a sun-loving crop plant! The Z-scheme of the Light Reactions: An Energy Diagram -2.0 reducing P700* FeS -1.5 -1.0 Em (volts) 0.5 1.0 1.5 2.0 cyt b Pheo PQ 0 ATP 2 H2O cyt f PC ADP+Pi 4 eO 2 + 4 H+ oxidizing P680 PS II eH+ NADP+ NADPH P680* -0.5 Fd FNR P700 PS I The Calvin Cycle has Three Phases P-C-C-C-C-C-P CO2 ribulose-1,5bisphosphate rubisco carboxylation ADP C-C-C-P 3-phosphoglycerate regeneration ATP sucrose for transport starch for storage reduction C-C-C-P glyceraldehyde3-phosphate ATP NADPH NADP+ ADP + Pi Let’s Do Some Stoichiometry: 3 x 5 = 15 C 3 ADP 3 P-C-C-C-C-C-P CO2 3 ribulose-1,5bisphosphate rubisco carboxylation 6 C-C-C-P 3-phosphoglycerate 6 3 ATP ATP 6 reduction NADPH 5 5 x 3 = 15 C 6 6 C-C-C-P NADP+ To take off 3 carbons: glyceraldehyde- 6 ADP + Pi sucrose for transport 6 3-phosphate 1 starch for storage regeneration complex shuffling More Stoichiometry: 3 ADP 3 P-C-C-C-C-C-P CO2 3 ribulose-1,5bisphosphate rubisco carboxylation 6 C-C-C-P 3 ATP 3-phosphoglycerate sucrose and 6 starch are not ATP 6 reduction 3-carbon NADPH 5 compounds! 6 6 C-C-C-P NADP+ To take off 3 carbons: glyceraldehyde- 6 ADP + Pi sucrose for transport 6 3-phosphate 1 starch for storage regeneration complex shuffling The Calvin Cycle and Light Reactions are interdependent H2O O2 Light Reactions thylakoid chlorophyll, etc. ADP + Pi NADP+ Calvin Cycle NADPH ATP rubisco, etc. stroma CO2 (CH2O)3 The Calvin Cycle cannot operate in darkness! “Dark Reactions?” Photosynthesis: Review and Expansion CO2 + H2O light chlorophyll O2 + CH2O Light Reactions: perhaps 25 steps ADP + P +NADP + H2O light chlorophyll We have been hiding considerable truth from you! Not 1 step… more like 50! O2 + NADPH2 + ATP Interdependent! Calvin Cycle Reactions: perhaps 25 steps AKA: Dark Reactions ATP + NADPH2 + CO2 In sum: CO2 + H2O CH2O + NADP + ADP + P light O2 + CH2O chlorophyll The light and Calvin cycle reactions are interdependent… no dark reactions! RuBisCO: an ancient enzyme with a modern problem RuBP + CO2 RuBisCO RuBisCO often constitutes up to 40% of the protein in a plant…to ensure enough photosynthesis is achieved 1% in air O=C=O RuBP + O2 20% in air O=O 2 x P-C-C-C (a triose relative) RuBisCO P-C-C-C (a triose relative) + P-C-C 2 x CO2 photorespiration • Early in evolution of photosynthesis the atmosphere was anaerobic, so RuBisCo evolved without a problem. • As photosynthesis was successful, competitive inhibition from oxygen was essentially a negative feedback. • Evolution has not yet replaced RuBisCO. • But several workarounds have evolved… C4 Photosynthesis: The first fixation is a 4-carbon compound Mesophyll Cell Bundle Sheath Cell regeneration C3 acid phosphoenol pyruvate HCO3pepc C4 acid plasmodesmata C3 acid Calvin cycle rubisco CO2 decarboxylation C4 acid carboxylation atm CO2 The C4 and C3 reactions are spatially separated C4 Zea mays Leaves bundle sheath mesophyll PEPc expression in leaf cs http://botit.botany.wisc.edu/images/130/Leaf/Zea_leaf_cross_section/ Major_vein_MC.jpg http://www.conabio.gob.mx/malezasdemexico/a steraceae/flaveria-trinervia/imagenes/rama.jpg RubisCO expression in leaf cs Flaveria bidentis http://www.uni-duesseldorf.de/home/Jahrbuch/2002/Grieshaber/Grafik/Grieshaber05.gif http://wings.buffalo.edu/academic/department/fnsm/ bio-sci/facultyart.GIFS/Berryart.gif Zea mays leaf cross section showing classic Kranz anatomy Zea mays leaf cross section These bulliform cells lose water and the leaf rolls…which way? C4 Photosynthesis: A cycle requiring ATP and NADPH NADP malic enzyme type Bundle Sheath Cell Mesophyll Cell ADP HCO3pepc carbonic anhydrase atm CO2 pyruvatephopsphate dikinase Pi CCCOOpyruvate NADPH NADP+ CCCCOOoxaloacetate -OOCCCCOOmalate malate dehydrogenase plasmodesmata P CCCOOphosphoenol pyruvate ATP CCCOOpyruvate NADPH malic enzyme NADP+ Calvin cycle rubisco CO2 -OOCCCCOOmalate The C4 and C3 reactions are spatially separated CAM Photosynthesis: Crassulacean Acid Metabolism At Night In Daylight starch triose phosphate phosphoenol pyruvate low pH HCO3- malic acid higher pH NADPH pepc NAD+ malate NADH malic oxaloacetate dehydrogenase atm CO2 starch Calvin cycle pyruvate rubisco CO2 malic acid malic enzyme NADP+ malate stomata open! stomata closed! The C4 and C3 reactions are temporally separated Sedum leaf cross-section (a CAM plant)Note the lack of palisade/spongy differentiation Sedum leaf cross-section (a CAM plant)Note the lack of Kranz anatomy
