Presentation on theme: "Photosynthesis The Source of most Biological Energy"— Presentation transcript:
1 Photosynthesis The Source of most Biological Energy Trapped in PhotosynthesisEnergy Converted to Chemical Bonds
2 Respiration: CH2O + O2 CO2 + H2O + ATP Photosynthesis: CH2O + O2 Krebs cyclemitochondrionmatrixCO2NADHATPETS + Ox PhosmitochondrioncristaeO2H2OATPglycolysiscytosolsugarpyruvatePhotosynthesis:CH2O + O2CO2 + H2O + lightsucrosesynthesiscytosolCalvin cyclechloroplaststromaCO2NADPHATPLR + P PhoschloroplastthylakoidO2H2OLightsugartriose
3 Light: An Energy Waveform With Particle Properties Too wavelengthvioletbluegreenyelloworangerednmwavelength (nm)10-9 metermeter!
4 Light: An Energy Waveform With Particle Properties Too wavelengthvisible spectrumnmwavelength (nm)10-9 metermeter!
5 White light: all the colors humans can see at once
6 Which side of our brains are we using? Which side of our brains are we using?
7 Leaf Pigments Absorb Most Colors White LightGreen is reflected!Leaf Pigments Absorb Most Colors
8 Light: An Energy Waveform With Particle Properties Too amplitudebrightnessintensityMany metric units for different purposesWe will use an easy-to-remember English unit: foot-candle0 fc = darkness100 fc = living room1,000 fc = CT winter day10,000 fc = June 21, noon, equator, 0 humidity
9 What wavelengths of light drive photosynthesis? Photosynthetic Rate100%Action Spectrumgreen light reflectedsome still drives photosynthesisvisible spectrumnmwavelength (nm)Light beyond 700 nm has insufficient energy to drive photosynthesis
10 Antenna Pigment Complex Photosystem IILightchlorophyll bP450energy transferluteinP470e-to: ETSzeaxanthinP480ß-caroteneP500Antenna Pigment ComplexlycopeneP510e-from: H2OIn each energy transfer some energy is lost as heat: 2nd law of thermodynamics.chlorophyll bP650But enough energy is passed to P680 to eject an electron to the electron transport system.chlorophyll aP680
11 Photosynthetic pigments are amphipathic Chlorophyll aChlorophyll bß-CaroteneZeaxanthinCH2CH3C2H5HCH3CHNMgOO=COCH3CH2CHOC2H5HCH3CHNMgCH3OO=COCH3H3CCH3CHCHCHOOHH3CCH3CHCHCOCHCH2CH3H2CCHCO=CH3COCHCH2CH3H2CCHCO=CH3CPhotosynthetic pigments are amphipathicLutein
12 What intensities of light drive photosynthesis? Reaction Rate100%Photosynthesisadd to reservegrowreproduceRespirationUsing reserves and may dieLight Intensity (fc), ,000 fccompensation pointThe example plant shown here “breaks even” at an intensity we have in our homes…a house plant!
13 What intensities of light drive photosynthesis? Reaction Rate100%Photosynthesis APhotosynthesis BRespirationShade tolerant plant dies in intense light!Light Intensity (fc), ,000 fccompensation pointsThe second example plant shown here cannot survive in our homes…it is a sun-loving crop plant!
14 The Z-scheme of the Light Reactions: An Energy Diagram reducing-2.0-1.5-1.0-0.50.51.01.52.0P700*FeSFdFNRe-H+NADP+NADPHP680*cyt bPheoPQEm (volts)cyt fATPPC2 H2OADP+PiP7004 e-PS IP680O2 + 4 H+PS IIoxidizing
15 The Calvin Cycle has Three Phases P-C-C-C-C-C-P ribulose-1,5-bisphosphateCO2regenerationcarboxylationrubiscoADPC-C-C-P3-phospho-glyceratereductionATPATPNADPHC-C-C-P glyceraldehyde-3-phosphateNADP+ADP + Pisucrose for transportstarch for storage
16 Let’s Do Some Stoichiometry: 3 P-C-C-C-C-C-P ribulose-1,5-bisphosphate CO23 x 5 = 15 C3regenerationcarboxylationrubisco3ADPC-C-C-P3-phospho-glycerate6complex shuffling6reduction3ATPATP6NADPH55 x 3 = 15 C6C-C-C-P glyceraldehyde-3-phosphate6NADP+To take off 3 carbons:6ADP + Pisucrose for transportstarch for storage61
17 sucrose and starch are not 3-carbon compounds! More Stoichiometry:3P-C-C-C-C-C-P ribulose-1,5-bisphosphateCO233ADPregenerationcarboxylationrubiscoC-C-C-P3-phospho-glycerate63ATPcomplex shufflingsucrose and starch are not 3-carbon compounds!6reductionATP6NADPH56C-C-C-P glyceraldehyde-3-phosphate6NADP+To take off 3 carbons:6ADP + Pisucrose for transportstarch for storage61
18 The Calvin Cycle cannot operate in darkness! “Dark Reactions?” The Calvin Cycle and Light Reactions are interdependentH2O O2Light Reactionsthylakoidchlorophyll, etc.ADP + Pi ATPNADP NADPHCalvin Cyclerubisco, etc.stromaCO (CH2O)3The Calvin Cycle cannot operate in darkness! “Dark Reactions?”
19 Photosynthesis: Review and Expansion We have been hiding considerable truth from you!Not 1 step… more like 50!lightCO2 + H2OO2 + CH2OchlorophyllLight Reactions: perhaps 25 stepslightADP + P +NADP +H2OO2+ NADPH2+ ATPchlorophyllInterdependent!Calvin Cycle Reactions: perhaps 25 stepsAKA: Dark ReactionsATP +NADPH2 +CO2CH2O+ NADP+ ADP + PlightIn sum:CO2 + H2OO2 + CH2OchlorophyllThe light and Calvin cycle reactions are interdependent… no dark reactions!
20 RuBisCO: an ancient enzyme with a modern problem RuBP + CO22 x P-C-C-C (a triose relative)1% in airO=C=ORuBisCO often constitutes up to 40% of the protein in a plant…to ensure enough photosynthesis is achievedRuBisCORuBP + O2P-C-C-C (a triose relative)+ P-C-C2 x CO220% in airO=OphotorespirationEarly 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…
21 C4 Photosynthesis: The first fixation is a 4-carbon compound Mesophyll CellBundle Sheath CellregenerationCalvin cycleC3 acidC3 acidphosphoenol pyruvaterubiscoplasmodesmataCO2HCO3-pepcdecarboxylationC4 acidC4 acidcarboxylationatmCO2The C4 and C3 reactions are spatially separated
22 C4 Leaves Zea mays PEPc expression in leaf cs bundle sheathmesophyllFlaveria bidentisRubisCO expression in leaf csPEPc expression in leaf cs