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Photosynthesis The Source of most Biological Energy

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Presentation on theme: "Photosynthesis The Source of most Biological Energy"— Presentation transcript:

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

2 Respiration: CH2O + O2 CO2 + H2O + ATP Photosynthesis: CH2O + O2
Krebs cycle mitochondrion matrix CO2 NADH ATP ETS + Ox Phos mitochondrion cristae O2 H2O ATP glycolysis cytosol sugar pyruvate Photosynthesis: CH2O + O2 CO2 + H2O + light sucrose synthesis cytosol Calvin cycle chloroplast stroma CO2 NADPH ATP LR + P Phos chloroplast thylakoid O2 H2O Light sugar triose

3 Light: An Energy Waveform With Particle Properties Too
wavelength violet blue green yellow orange red nm wavelength (nm) 10-9 meter meter!

4 Light: An Energy Waveform With Particle Properties Too
wavelength visible spectrum nm wavelength (nm) 10-9 meter meter!

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 Light Green is reflected! Leaf Pigments Absorb Most Colors

8 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

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

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

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

12 What intensities of light drive photosynthesis?
Reaction Rate 100% Photosynthesis add to reserve grow reproduce Respiration Using reserves and may die Light Intensity (fc) , ,000 fc compensation point The 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 Rate 100% Photosynthesis A Photosynthesis B Respiration Shade tolerant plant dies in intense light! Light Intensity (fc) , ,000 fc compensation points The 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 -0.5 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 ATP PC 2 H2O ADP+Pi P700 4 e- PS I P680 O2 + 4 H+ PS II oxidizing

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

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

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

18 The Calvin Cycle cannot operate in darkness! “Dark Reactions?”
The Calvin Cycle and Light Reactions are interdependent H2O O2 Light Reactions thylakoid chlorophyll, etc. ADP + Pi ATP NADP NADPH Calvin Cycle rubisco, etc. stroma CO (CH2O)3 The 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! light CO2 + H2O O2 + CH2O chlorophyll Light Reactions: perhaps 25 steps light ADP + P + NADP + H2O O2 + NADPH2 + ATP chlorophyll Interdependent! Calvin Cycle Reactions: perhaps 25 steps AKA: Dark Reactions ATP + NADPH2 + CO2 CH2O + NADP + ADP + P light In sum: CO2 + H2O O2 + CH2O chlorophyll The light and Calvin cycle reactions are interdependent… no dark reactions!

20 RuBisCO: an ancient enzyme with a modern problem
RuBP + CO2 2 x P-C-C-C (a triose relative) 1% in air O=C=O RuBisCO often constitutes up to 40% of the protein in a plant…to ensure enough photosynthesis is achieved RuBisCO RuBP + O2 P-C-C-C (a triose relative) + P-C-C 2 x CO2 20% in air O=O 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…

21 C4 Photosynthesis: The first fixation is a 4-carbon compound
Mesophyll Cell Bundle Sheath Cell regeneration Calvin 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

22 C4 Leaves Zea mays PEPc expression in leaf cs
bundle sheath mesophyll Flaveria bidentis RubisCO expression in leaf cs PEPc expression in leaf cs

23 Zea mays leaf cross section showing classic Kranz anatomy

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

25 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-phosphoenol pyruvate P CCCOO- pyruvate pyruvate-phopsphate dikinase Calvin cycle NADPH rubisco HCO3- plasmodesmata malic enzyme CO2 pepc NADPH Pi NADP+ NADP+ CCCCOO- oxaloacetate carbonic anhydrase -OOCCCCOO- malate -OOCCCCOO- malate malate dehydrogenase atm CO2 The C4 and C3 reactions are spatially separated

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

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

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


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