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PS Lecture OutlineI. Introduction
A. StructuresB. Net Reaction
II. Overview of PSA. Rxns in the chloroplastB. pigments
III. Closer looksA. LD RxnsB. LI Rxns
1. non-cyclic e- flow2. cyclic e- flow3. chemiosmosis
C. Calvin CycleD. Alternative C-fixations
IV. Variables in PS effectiveness
Vein
Leaf cross section
Mesophyll
CO2 O2Stomata
A. Structures of PS• Site of PS in plants:
• mostly in leaves• in chloroplasts
Inside the chloroplast
• Identify the structures in the diagram
Chloroplast
Mesophyll
5 µm
Outer membrane
Intermembrane space
Inner membrane
Thylakoid space
Thylakoid
GranumStroma
1 µm
• Chloroplasts
• thylakoids
• grana
• stroma
6H2O + 6CO2 ------> C6H12O6+ 6O26 waters
6 carbon dioxides(plus light E, makes...)
1 glucose6 oxygen
B. The Net Reaction of Photosynthesis
Net Reaction• hydrolysis
• e- of H --> sugar• O --> O2
6 CO2 12 H2OReactants:
Products: C6H12O6 6 H2O 6 O2
Figure 10.4Photosynthesis is a redox process
Water is oxidized, carbon dioxide is reduced
• we will stay (mostly) conceptual
• follow the energy
II. PS Overview
• Occur in the grana1. capture photons2. split water3. release oxygen4. produce ATP
a. “photophosphoryllation driven by chemiosmosis”b. E transfer
5. form NADPH• E transfer
A. Light Dependant Rxns
• aka The Calvin cycle• in the stroma1. forms sugar from carbon dioxide2. uses ATP for energy3. uses NADPH for reducing power
B. Light Independent Rxns
PS Overview
PS Overview
PS Overview
• How does the chloroplast absorb light?
• Pigments
• chlorophyll a,b
• accessory pigments
Photosynthetic Pigments: The Light Receptors
III. Closer look at LD Rxns
Excited state
Ene
rgy
of e
lect
ion
Heat
Photon (fluorescence)
Chlorophyll molecule
Ground statePhoton
e–
Figure 10.11 A
• When a pigment absorbs light
• ground state --> excited state (unstable)
Excitation of Chlorophyll by Light
Photosystems• Light harvesting
complexes• aka “antenna
pigment mols”• pigment mols
bound by proteins
• funnel energy to reaction center
• e- gets bumped• p680 (PSII)• p700 (PSI)
Primary election acceptor
Photon
Thylakoid
Light-harvesting complexes
Reaction center
Photosystem
STROMA
Thyl
akoi
d m
embr
ane
Transfer of energy
Special chlorophyll a
molecules
Pigment molecules
THYLAKOID SPACE (INTERIOR OF THYLAKOID)Figure 10.12
e–
Mill makes ATP
ATP
e–
e–e–
e–
e–
Phot
on
Photosystem II Photosystem I
e–
e–
NADPH
Phot
on
Figure 10.14
Analogy for the Lt Rxns
Noncyclic electron flow• Produces NADPH, ATP, and oxygen
© 2014 Pearson Education, Inc.
The biomass (dry weight) of a tree comes primarily from
A. soil. B. water. C. air. D. organic fertilizer (manure, detritus). E. light.
© 2014 Pearson Education, Inc.
The light reactions, which involve the very hydrophobic chlorophyll, are located here in the chloroplast.
A.
B.C. (lumen)
E.
D.
© 2014 Pearson Education, Inc.
What colors of light will drive photosynthesis by green plants most efficiently?
A. red only B. yellow only C. green only D. blue only E. red and blue
© 2014 Pearson Education, Inc.
How are the light reactions and the Calvin cycle connected?
A. The light reactions provide ATP to the Calvin cycle, and the Calvin cycle provides NADPH for the light reactions.
B. The light reactions provide ATP and NADPH to the Calvin cycle, and the Calvin cycle returns ADP and NADP+ to the light reactions.
C. The light reactions provide ATP and NADPH to the Calvin cycle, and the Calvin cycle returns reduced sugars to the light reactions.
D. The light reactions provide NADPH to the Calvin cycle, and the Calvin cycle provides RuBP to the light reactions.
E. The light reactions provide RuBP to the Calvin cycle, and the Calvin cycle returns G3P to the light reactions.
• Occurs:
• Sim to Citric Acid Cycle (aka Krebs) in CR
• opposite of anaerobic glycolysis
• 3 phases
• C-fixation
• Reduction
• Regeneration of the CO2 acceptor
Calvin Cycle
(G3P)
Input(Entering one
at a time)CO2
3
RubiscoShort-lived
intermediate
3 P P
3 P PRibulose bisphosphate
(RuBP)
P
3-Phosphoglycerate
P6 P
6
1,3-Bisphoglycerate6 NADPH
6 NADPH+
6 P
P6
Glyceraldehyde-3-phosphate (G3P)
6 ATP
3 ATP
3 ADP CALVIN CYCLE
P5
P1 G3P (a sugar)Output
LightH2O CO2
LIGHTREACTION
ATP
NADPH
NADP+
ADP
[CH2O] (sugar)
CALVIN CYCLE
Figure 10.18
O2
6 ADP
Glucose andother organiccompounds
Phase 1: Carbon fixation
Phase 2:Reduction
Phase 3:Regeneration ofthe CO2 acceptor
(RuBP)
The Calvin Cycle
The Calvin Cycle• Starts w/ CO2 + enzyme Rubisco +RuBP
• 3 “turns” of Calvin make...
• 3-C sugar
• 6 “turns” = 1 glucose
The Calvin Cycle• Three phases...
• Fixation
• CO2 + RuBP + Rubisco
• Reduction
• requires ATP (for E)
• requires H (from NADPH)
• produces 3-C sugars: G3P
• 1/6 of which form Glu
• Regeneration
• 5/6 of 3-C sugars regenerate RuBP
• requires ATP
• aka Cyclic Phosphoryllation
• Under certain conditions
• ATP deficit
• excess NADPH, deficit of NADP+
• bumped e-’s take an alternative path
• generates ATP
Cyclic Electron Flow
• Only photosystem I is used• Only ATP is produced (no O2 or NADPH)
Primary acceptor
Pq
Fd
Cytochrome complex
Pc
Primary acceptor
Fd
NADP+
reductaseNADPH
ATPFigure 10.15 Photosystem II Photosystem I
NADP+
Cyclic Electron Flow
Alternative C-Fixations• What do plants do on hot, arid days?
• close their stomata
• What happens to PS reactants/prods?
• water conserved
• less CO2
• O2 build up
• Leads to Photorespiration
• O2 substitutes for CO2 in the active site of the enzyme rubisco
• Rate PS decreases
Minimizing Photorespiration
• C4 plants
• avoid photorespiration spatially
• CO2 stored as 4-C compounds
• stored in mesophyll cells• exported to bundle
sheath cells
• release CO2 to the Calvin cycle
CO2
Mesophyll cell
Bundle- sheath
cell
Vein (vascular tissue)
Photosynthetic cells of C4 plant
leaf
Stoma
Mesophyll cell
C4 leaf anatomy
PEP carboxylase
Oxaloacetate (4 C) PEP (3 C)
Malate (4 C)
ADP
ATP
Bundle- Sheath
cell CO2
Pyruvate (3 C)
CALVIN CYCLE
Sugar
Vascular tissue
Figure 10.19
CO2
C4 Path
Minimizing Photorespiration
• CAM plants• avoid photorespiration
temporally• Open their stomata at
night
• incorporating CO2 into organic acids
• CO2 released during the day to CC
Spatial separation of steps. In C4 plants,
carbon fixation and the Calvin cycle occur in
different types of cells.
(a) Temporal separation of steps. In CAM plants, carbon fixation and the
Calvin cycle occur in the same cells
at different times.
(b)
PineappleSugarcane
Bundle- sheath cell
Mesophyll Cell
Organic acid
CALVIN CYCLE
Sugar
CO2 CO2
Organic acid
CALVIN CYCLE
Sugar
C4 CAM
CO2 incorporated into four-carbon organic acids
(carbon fixation)
Night
Day
1
2 Organic acids release CO2 to
Calvin cycle
Figure 10.20
C4 vs CAM
Effect of Light Intensity
• low light => not enough ATP, NADPH
• what would be rate limiting step in Calvin Cycle?
• unusual unless the plant is heavily shaded
Effect of CO2 Concentration
• low CO2 => what would be rate-limiting step?
• this is a common limiting factor
Effect of Temperature
• low temps => rate of rxn = ____
• high temps => CO2 fixation doesn’t work