Chapter 19 Photosynthesis 2

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Lecture 15
Chapter 19 Photosynthesis 2
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The Thylakoid Membrane
PSII
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Photosystem II
H2O oxidized to O2
Plastoquinone (PQ) reduced.
H ions translocated
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The Thylakoid Membrane
PSII
Cyt b/complex
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The cyt bf complex
Plastocyanin (PC) Aceepts electrons from The cyt
bf complex.
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The Thylakoid Membrane
PSII
PSI
Cyt b/complex
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Photosystem I
NADPH formed
PC donates electrons
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The Thylakoid Membrane
PSI
PSII
Cyt b/complex
ATP Synthase
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CF1 coupling Factor synthesizes ATP
CFo proton channel
ATP synthase
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• Chemiosmosis revisited
• Light via electron transport can produce a proton
  gradient.
• The protein gradient alone can provide energy for
  ATP formation.

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• Light via electron transport
• can produce a proton gradient.

Lt
Uncoupler
pH electrode
H
Dk
Time
Chloroplast
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• A pH gradient can
• cause ATP formation

• Lower the internal
• pH to 4.

b. Raise outside pH to 8 add ADP.

• Observe ATP
• formation.

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Carbon Dioxide Fixation The Calvin Cycle.
3 ATP 2 NADPH are required to fix 1 CO2 into
carbohydrate
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Calvin cycle
2 3phosphoglycerate
6C
2 ATP
CO2
ribulose-bis-phosphate carboxylase (RUBISCO)
1,3-bisphosphglycerate
Ribulose-1,5-bisphosphate (5C)
2NADPH
1 ATP
glucose
3-phosphoglyceraldehde
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Melvin Calvin Nobel Prize 1961 Dark Reactions
of Photosynthesis Used 14C And paper
chromatography
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CO2
2 3-Pglycerate
Ribulose-1,5-bisP
RUBISCO
2 3-Pglyceraldehyde
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RUBISCO can fix O2 as well as CO2 ?
photorespiration
Normal
CO2
2 3-Pglycerate
Ribulose-1,5-bisP
RUBISCO
2 3-Pglyceraldehyde
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Waste some of the ATP and NADPH formed in the
Light reactions.
Glycolate
Phosphoglycolate
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C4 CO2 pump
CO2 released and Refixed by Calvin cycle
CO2
C4 acids
Mesophyll cells Bundle Sheath Cells
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Mesophyll cells CO2 is fixed into C4 acids.
The C4 acids are transported to the bundle
sheath cells where
It is released and refixed by the Calvin cycle.
Why? To increase the CO2 concentration in
the vicinity of RUBISCO.