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Photosynthesis

Photosynthesis. The Source of most Biological Energy Trapped in Photosynthesis Energy Converted to Chemical Bonds. Light: An Energy Waveform With Particle Properties Too. wavelength. violet. blue. green. yellow. orange. red. 400 500 600 700 nm.

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Photosynthesis

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  1. Photosynthesis The Source of most Biological Energy Trapped in Photosynthesis Energy Converted to Chemical Bonds

  2. 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!

  3. Light:An Energy Waveform With Particle Properties Too wavelength visible spectrum 400 500 600 700 nm wavelength (nm) 10-9 meter 0.000000001 meter!

  4. White Light Green is reflected! Leaf Pigments Absorb Most Colors

  5. 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

  6. 100% Photosynthetic Rate 0 What wavelengths of light drive photosynthesis? Action Spectrum green light reflected some still drives photosynthesis visible spectrum 400 500 600 700 nm wavelength (nm) Light beyond 700 nm has insufficient energy to drive photosynthesis

  7. Photosystem II chlorophyll b P450 lutein P470 to: ETS zeaxanthin energy transfer e- P480 ß-carotene P500 from: H2O lycopene P510 e- chlorophyll b P650 chlorophyll a P680 Light Antenna Pigment Complex In each energy transfersome energy is lost as heat:2nd law of thermodynamics. But enough energyis passed to P680 to eject an electron to the electron transport system.

  8. CH2 CH2 CH3 CHO HC HC HO H H CH3 CH3 C2H5 C2H5 H3C H3C CH3 CH3 N N N N CH CH H3C H3C Mg Mg H H H H HC HC N N H3C H3C N N CH3 CH3 H H HC HC H H CH CH H H H2C H2C HC HC O O CH2 CH2 O=COCH3 O=COCH3 C C CH3 CH3 C CH3 C CH3 O=C O=C HC HC O O CH CH H2C H2C HC HC CH CH CH CH C C C C H3C H3C H3C H3C CH2 CH2 CH CH H2C H2C HC HC CH2 CH2 CH CH CH CH H3C H3C C C CH2 CH2 CH CH H2C H2C HC HC CH3 CH3 CH2 CH2 H3C H3C CH CH H3C H3C H3C H3C CH2 CH2 H3C H3C OH H2C H2C CH2 CH2 HC HC H3C H3C CH3 CH3 Chlorophyll a Chlorophyll b ß-Carotene Zeaxanthin Photosynthetic pigments are amphipathic Lutein

  9. 100% Reaction Rate 0 0 10 100 1,000 10,000 fc Light Intensity (fc) What intensities of light drive photosynthesis? Photosynthesis add to reserve grow reproduce Respiration Using reserves and may die compensation point The example plant shown here “breaks even” at an intensity we have in our homes…a house plant!

  10. 100% Reaction Rate 0 0 10 100 1,000 10,000 fc Light Intensity (fc) What intensities of light drive photosynthesis? Photosynthesis A Photosynthesis B Respiration Shade tolerant plant dies in intense light! compensation points The second example plant shown here cannot survive in our homes…it is a sun-loving crop plant!

  11. The Light Reactions: An Energy Diagram reducing -2.0 -1.5 -1.0 -0.5 0 0.5 1.0 1.5 2.0 P700* FeS Fd FNR e- H+ NADP+ NADPH P680* cyt b Pheo PQ Em (volts) cyt f PC ATP 2 H2O ADP+Pi P700 PS I 4 e- P680 O2 + 4 H+ PS II oxidizing

  12. carboxylation regeneration reduction The PCR Cycle has Three Phases P-C-C-C-C-C-P ribulose-1,5-bisphosphate CO2 rubisco ADP C-C-C-P 3-phospho-glycerate ATP ATP NADPH C-C-C-P glyceraldehyde-3-phosphate NADP+ ADP + Pi sucrose for transport starch for storage

  13. carboxylation regeneration reduction Let’s Do Some Stoichiometry: 3 P-C-C-C-C-C-P ribulose-1,5-bisphosphate CO2 3 x 5 = 15 C 3 rubisco 3 ADP 6 C-C-C-P 3-phospho-glycerate complex shuffling 6 3 ATP ATP 6 NADPH 5 5 x 3 = 15 C 6 6 C-C-C-P glyceraldehyde-3-phosphate NADP+ To take off 3 carbons: 6 ADP + Pi sucrose for transport starch for storage 6 1

  14. carboxylation regeneration reduction More Stoichiometry: 3 P-C-C-C-C-C-P ribulose-1,5-bisphosphate CO2 3 3 ADP rubisco 6 C-C-C-P 3-phospho-glycerate 3 ATP complex shuffling sucrose and starch are not 3-carbon compounds! 6 ATP 6 NADPH 5 6 6 C-C-C-P glyceraldehyde-3-phosphate NADP+ To take off 3 carbons: 6 ADP + Pi sucrose for transport starch for storage 6 1

  15. The PCR Cycle and Light Reactions are interdependent H2O O2 Light Reactions thylakoid chlorophyll, etc. ADP + Pi ATP NADP+ NADPH rubisco, etc. PCR Cycle stroma CO2 (CH2O)3 The PCR Cycle cannot operate in darkness!“Dark Reactions?”

  16. O=C=O O=O RuBisCO: an ancient enzyme with a modern problem RuBisCO RuBP + CO2 2 x P-C-C-C (Phosphoglycerate) 1% in air RuBisCO often constitutes up to 50% of the protein in a plant…to ensure enough photosynthesis is achieved RuBisCO RuBP + O2 P-C-C-C (a Phosphoglycerate) + P-C-C 2 x CO2 20% in air 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…

  17. C4 Photosynthesis: The first fixation is a 4-carbon compound Mesophyll Cell Bundle Sheath Cell regeneration PCR cycle C3 acid C3 acid phosphoenol pyruvate rubisco plasmodesmata CO2 HCO3- pepc decarboxylation C4 acid C4 acid carboxylation atm CO2 The C4 and C3 reactions are spatially separated

  18. Zea mays PEPc expression in leaf cs http://www.conabio.gob.mx/malezasdemexico/asteraceae/flaveria-trinervia/imagenes/rama.jpg RubisCO expression in leaf cs Flaveria bidentis http://wings.buffalo.edu/academic/department/fnsm/bio-sci/facultyart.GIFS/Berryart.gif http://www.uni-duesseldorf.de/home/Jahrbuch/2002/Grieshaber/Grafik/Grieshaber05.gif C4Leaves bundle sheath mesophyll http://botit.botany.wisc.edu/images/130/Leaf/Zea_leaf_cross_section/Major_vein_MC.jpg

  19. Zea mays leaf cross section showing classic Kranz anatomy

  20. Zea mays leaf cross section These bulliform cells lose water and the leaf rolls…which way?

  21. P CCCOO-phosphoenol pyruvate C4 Photosynthesis: A cycle requiring ATP and NADPH NADP malic enzyme type Mesophyll Cell Bundle Sheath Cell ADP ATP CCCOO- pyruvate CCCOO- pyruvate pyruvate-phopsphate dikinase PCRcycle NADPH rubisco HCO3- malic enzyme plasmodesmata CO2 pepc NADPH Pi NADP+ NADP+ CCCCOO- oxaloacetate -OOCCCCOO- malate carbonic anhydrase -OOCCCCOO- malate malate dehydrogenase atm CO2 The C4 and C3 reactions are spatially separated

  22. CAM Photosynthesis: Crassulacean Acid Metabolism starch At Night In Daylight starch PCR cycle triose phosphate pyruvate rubisco CO2 phosphoenol pyruvate low pH higher pH NADPH malic acid malic acid HCO3- malic enzyme pepc malate NAD+ NADH NADP+ malic dehydrogenase malate oxaloacetate atm CO2 stomata open! stomata closed! The C4 and C3 reactions are temporally separated

  23. Sedum leaf cross-section (a CAM plant) Note the lack of palisade/spongy differentiation

  24. Sedum leaf cross-section (a CAM plant) Note the lack of Kranz anatomy

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