Monday

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• Mondays Topics
• Overview of photosynthesis
• Key early photosynthesis experiments
• Photosynthesis light reactions

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From which molecule does the O2 released by
plants come from? What happens to H20 during
photosynthesis? (more than one answer might be
correct) a. Oxidized b. Reduced c.
Activated d. Looses electrons e. Gains
electrons Which are the energy rich compounds
generated during the light reactions?
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• Todays Topics
• Electron transfer during the light reactions
• Regulation of photosynthesis
• Evolution of photosynthetic systems

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The Electron Transfer Process
Energy
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Duysens Amesz (1962)
PSI PSII Light
Darkness
Oxidized State
PSI Light
Cytochrome
PSI Light
Reduced State
Time
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Z-Scheme Electron transfers (redox reactions)
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Photosynthesis Light Reactions
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Reactions of Plastoquinones
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Photosynthesis Light Reactions
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Electron Transfer in the Cytochrome b6f Complex
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Electron Transfer in the Cytochrome b6f Complex
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Photosynthesis Light Reactions
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Herbicides and the study of photosynthesis
Blocks electron transfer in PSI
Blocks electron transfer to plastoquinone
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Excercises
What will the status of the plastoquinone pool in
DCMU treated plants? a. Reduced b.
Oxidiced What will the status of the
plastocyanin pool be in Paraquot treated
plants? a. Reduced b. Oxidiced
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Photosynthesis Light Reactions
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• Todays Topics
• Electron transfer during the light reactions
• Regulation of photosynthesis
• Evolution of photosynthetic systems

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Problems with the electron transfer process

1. Excess energy absorbance
2. Electron balances between PSI and PSII

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Problems with the electron transfer process
Energy
H20
2 H ½ O2
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PHOTOPROTECTION
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Nonphotochemical Quenching

1. Reorganization of antenna complexes
2. Special carotenoids xantophylls
3. Thylakoid lumen pH

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Problems with the electron transfer process

1. Excess energy absorbance
2. Electron balances between PSI and PSII

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Energy partitioning between photosystems
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• Topics
• Electron transfer during the light reactions
• Regulation of photosynthesis
• Evolution of photosynthetic systems

26
How does a plant make more chloroplasts?
Where are chloroplast proteins made?
Where do the chloroplasts come from?
Do all chloroplasts in all algae and plants have
the same origin?
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What are the main open questions about the origin
of oxygenic photosynthesis? Which are the
current hypothesis to explain the beginning of
oxygenic photosynthesis?
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Next lecture -Carbon reactions of photosynthesis
Light Reactions
Carbon Reactions
ATP NADPH
H20 O2
CO2 CH20