Photosynthesis

1
Photosynthesis

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

2
Respiration
Krebs cycle mitochondrion matrix
ETS Ox Phos mitochondrion cristae
?CO2 ?NADH? ?ATP
?O2 ?H2O ?ATP
glycolysis cytosol
sugar?
?pyruvate?
Photosynthesis
sucrose synthesis cytosol
Calvin cycle chloroplast stroma
LR P Phos chloroplast thylakoid
?CO2 ?NADPH? ?ATP?
?O2 ?H2O ?Light
sugar?
?triose?
3
Light An Energy Waveform With Particle
Properties Too
wavelength
violet
blue
green
yellow
orange
red
400 500 600
700 nm
wavelength (nm)
10-9 meter
0.000000001 meter!
4
Light An Energy Waveform With Particle
Properties Too
wavelength
visible spectrum
400 500 600
700 nm
wavelength (nm)
10-9 meter
0.000000001 meter!
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White light all the colors humans can see at once
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Which side of our brains are we using?
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White Light
Green is reflected!
Leaf Pigments Absorb Most Colors
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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
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What wavelengths of light drive photosynthesis?
Action Spectrum
green light reflected
some still drives photosynthesis
visible spectrum
400 500 600
700 nm
wavelength (nm)
Light beyond 700 nm has insufficient energy to
drive photosynthesis
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Photosystem II
Light
Antenna Pigment Complex
In each energy transfersome energy is lost as
heat2nd law of thermodynamics.
But enough energyis passed to P680 to eject an
electron to the electron transport system.
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Chlorophyll a
Chlorophyll b
ß-Carotene
Zeaxanthin
Photosynthetic pigments are amphipathic
Lutein
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What intensities of light drive photosynthesis?
Photosynthesis
add to reserve grow reproduce
Respiration
Using reserves and may die
compensation point
The example plant shown here breaks even at an
intensity we have in our homesa house plant!
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What intensities of light drive photosynthesis?
Photosynthesis A
Photosynthesis B
Respiration
Shade tolerant plant dies in intense light!
compensation points
The second example plant shown here cannot
survive in our homesit is a sun-loving crop
plant!
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The Z-scheme of the Light Reactions An Energy
Diagram
reducing
-2.0 -1.5 -1.0 -0.5 0 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
PC
ATP
2 H2O
ADPPi
P700
PS I
4 e-
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
rubisco
ADP
C-C-C-P 3-phospho-glycerate
ATP
ATP
NADPH
C-C-C-P glyceraldehyde-3-phosphate
NADP
ADP Pi
sucrose for transport starch for storage
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Lets Do Some Stoichiometry
3
P-C-C-C-C-C-P ribulose-1,5-bisphosphate
CO2
3 x 5 15 C
3
rubisco
ADP
3
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C-C-C-P 3-phospho-glycerate
complex shuffling
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ATP
3
ATP
6
NADPH
5
5 x 3 15 C
6
6
C-C-C-P glyceraldehyde-3-phosphate
NADP
To take off 3 carbons
ADP Pi
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sucrose for transport starch for storage
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1
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More Stoichiometry
3
P-C-C-C-C-C-P ribulose-1,5-bisphosphate
CO2
3
ADP
3
rubisco
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C-C-C-P 3-phospho-glycerate
ATP
3
complex shuffling
sucrose and starch are not 3-carbon compounds!
6
ATP
6
NADPH
5
6
6
C-C-C-P glyceraldehyde-3-phosphate
NADP
To take off 3 carbons
ADP Pi
6
sucrose for transport starch for storage
6
1
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The Calvin Cycle and Light Reactions are
interdependent
H2O O2
Light Reactions
thylakoid
chlorophyll, etc.
ADP Pi ATP
NADP NADPH
rubisco, etc.
Calvin Cycle
stroma
CO2 (CH2O)3
The Calvin Cycle cannot operate in
darkness!Dark Reactions?
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Photosynthesis Review and Expansion
We have been hiding considerable truth from
you! Not 1 stepmore like 50!
light
O2 CH2O
CO2 H2O
chlorophyll
Light Reactions perhaps 25 steps
light
H2O
ATP
NADP
ADP P
NADPH2
O2
chlorophyll
Interdependent!
Calvin Cycle Reactions perhaps 25 steps
AKA Dark Reactions
CO2
CH2O
NADPH2
NADP
ATP
ADP P
light
In sum
CO2 H2O
O2 CH2O
chlorophyll
The light and Calvin cycle reactions are
interdependentno dark reactions!
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RuBisCO an ancient enzyme with a modern problem
RuBisCO
RuBP CO2
2 x P-C-C-C (a triose relative)
1 in air
RuBisCO often constitutes up to 40 of the
protein in a plantto ensure enough
photosynthesis is achieved
RuBisCO
RuBP O2
P-C-C-C (a triose relative) P-C-C
2 x CO2
20 in air
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

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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
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Zea mays
C4 Leaves
bundle sheath
mesophyll
http//botit.botany.wisc.edu/images/130/Leaf/Zea_l
eaf_cross_section/Major_vein_MC.jpg
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Zea mays leaf cross section showing classic Kranz
anatomy
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Zea mays leaf cross section
These bulliform cells lose water and the leaf
rollswhich way?
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C4 Photosynthesis A cycle requiring ATP and NADPH
NADP malic enzyme type
Mesophyll Cell
Bundle Sheath Cell
ADP
ATP
CCCOO- pyruvate
CCCOO- pyruvate
Calvincycle
pyruvate-phopsphate dikinase
NADPH
rubisco
HCO3-
plasmodesmata
malic enzyme
CO2
pepc
NADPH
Pi
NADP
NADP
CCCCOO- oxaloacetate
-OOCCCCOO- malate
carbonic anhydrase
-OOCCCCOO- malate
malate dehydrogenase
atm CO2
The C4 and C3 reactions are spatially separated
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CAM Photosynthesis Crassulacean Acid Metabolism
At Night
In Daylight
starch
Calvin cycle
triose phosphate
pyruvate
rubisco
CO2
phosphoenol pyruvate
low pH
higher pH
NADPH
malic acid
malic acid
HCO3-
malic enzyme
pepc
malate
NAD
NADH
NADP
malic dehydrogenase
malate
oxaloacetate
atm CO2
stomata open!
stomata closed!
The C4 and C3 reactions are temporally separated
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Sedum leaf cross-section (a CAM plant)
Note the lack of palisade/spongy differentiation
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Sedum leaf cross-section (a CAM plant)
Note the lack of Kranz anatomy