Announcements, March 12 Please remove homework from folders One homework and 2 quizzes (Q14, Q18)...
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Transcript of Announcements, March 12 Please remove homework from folders One homework and 2 quizzes (Q14, Q18)...
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Announcements, March 12• Please remove homework from folders• One homework and 2 quizzes (Q14, Q18) without names
still unclaimed – please see me to claim.• Reading for today: pp. 288-302 on photosynthesis; pp.
302-307 will not be covered due to snow day.• Review Session from 4-5 PM, March 13 in BR 203• Exam 2 on Wednesday, March 14 over the same
material as before.• Reading for Friday, March 16: pp. 318-358 on
intracellular trafficking
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Chloroplast Ultrastructure
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Photosynthesis Overview• Light + 3 CO2 + 6 H2O → C3H6O3 + 3 O2 + 3 H2O• Function: ATP synthesis and synthetic rxns• Energy source: sunlight• Energy conversion:
– solar H+ gradient ATP– H2O electron transport NADPH
• Carbon source: CO2
• Electron source: H2O• Intermediate electron acceptor: NADP+
• Byproduct: O2
Reduced C:3C sugar
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Energy Transduction reactions:Photoreduction (NADPH synthesis)
Photophosphorylation (ATP synthesis)
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NADP+ and NADPH
Carry e- in syntheticreactions, whereasNAD+/NADP usedin degradative rxns.
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Absorption spectra of plant pigments
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Chlorophyll
Chlorophyll is special because it can accept a low energy electron and donate
a high energy electron.
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Light Harvesting Complex
1. Heat,light2.
3.
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Fate of light energy when e* eo
1. Energy is lost as heat and lower energy light.
2. Resonance energy transfer to an electron in an adjacent pigment molecule.
3. Photochemical reduction, where e* is itself transferred to a carrier (only in reaction center chlorophyll).
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Resonance Energy Transfer to Adjacent Pigments
e*
eo
e*
eo
e*
eo
e*
eo
Antenna chlorophyllsReaction center
chlorophyll P680PSII
Groundstate
Excitedstate
photon
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Photochemical Reduction:e* is transferred to NADP+
e*
eo
Reaction centerchlorophyll P680
PSII
e
H2O 2H+ + O2
e*
e*
eo
ChlorophyllP700PSI
e* e*
Electron transportSystem (ETS)
photonETS
NADP+
NADPHOEC
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Energy conversion in thylakoid MB
AnalogousTo RCIII
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The Z Scheme: Steps
1. Water splitting: 2 H2O → 4 H+, O2 to lumen
2. P680o P680* (PSII)3. Electron transfer to P700o (PSI)4. 4 H+ pumped to lumen through cytochrome b6/f
5. P700o P700* (PSI)6. Electron transfer to ferredoxin7. Ferredoxin-NADP+ reductase catalyzes: 2 NADP+ +
2 H+stroma + 2 e- 2 NADPH
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Understanding how the water-splitting enzyme works is a major unsolved problem,
with practical applications
4
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Z scheme
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Photophosphorylation(Light-driven ATP synthesis)
Current estimates (know this):• pHlumen = 6• pHstroma = 8 pH = -2 (in-out)• Em = +30 mV (flow of Mg2+ and
Cl- balances much of flow of H+)• pmf = 30 - 60 mV(-2) = +150 mV• 4 H+ flow/ATP through CF0CF1
ATP synthase• 4 e- Z scheme 2 ATP, 2
NADPH• But need 3 ATP/2 NADPH in
Calvin cycle, so cyclic electron flow occurs:
H+ Cl-
H+ H+ Mg2+
lumen
stroma
lumen
stroma
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Cyclic e- Flow• Regulates NADPH/ATP
formed (need 2:3).• 2 electrons flow back
through cyt b6/f to P700, pumping 4 H+ into lumen
• 2 photons re-excite the 2 electrons.
• No water oxidized and no O2 released, since PSII not involved.
NADP+
PSI
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Photosynthesis Reactions(Don’t memorize)
1. Energy transduction reactions (Equation 11-14)26 photons + 9 ADP + 9 Pi + 6 NADP+ + 6 H2O 3 O2 + 9 ATP + 6 NADPH + 3 H2O
2. Calvin cycle reactions (Equation 11-13)3 CO2 + 9 ATP + 6 NADPH + 6 H2O C3H6O6 + 6 NADP+ + 9 ADP + 9 Pi
3. Overall (Equation 11-16):26 photons + 3 CO2 + 6 H2O C3H6O6 + 3 O2 + 3 H2O
What % of mass of C3H6O6 comes from CO2 ?MW of CO2 is 44, of H2O is 18, of C3H6O6 is 186.
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Carbon fixation
occurs in the
stroma