overview: the process that feeds the biosphere photosynthesis is the process that converts solar...
TRANSCRIPT
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Overview: The Process That Feeds the Biosphere
• Photosynthesis is the process that converts solar energy into chemical energy
• Directly or indirectly, photosynthesis nourishes almost the entire living world
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• Autotrophs sustain themselves without eating anything derived from other organisms
• Autotrophs are the producers of the biosphere, producing organic molecules from CO2 and other inorganic molecules
• Almost all plants are photoautotrophs, using the energy of sunlight to make organic molecules from H2O and CO2
Autotrophs
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(a) Plants
(c) Unicellular protist10 µm
1.5 µm
40 µm(d) Cyanobacteria
(e) Purple sulfur bacteria
(b) Multicellular alga
Photosynthesis occurs in plants,
algae, certain other protists, and some prokaryotes
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• Heterotrophs obtain their organic material from other organisms
• Heterotrophs are the consumers of the biosphere
• Almost all heterotrophs, including humans, depend on photoautotrophs for food and O2
Heterotrophs
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The Two Stages of Photosynthesis: A Preview
• Photosynthesis consists of the light reactions (the photo part) and Calvin cycle (the synthesis part)
• The “light” reactions are in the thylakoids
• The Calvin cycle is in the stroma
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1 µm
Thylakoidspace
Chloroplast
GranumIntermembranespace
Innermembrane
Outermembrane
Stroma
Thylakoid
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• The “light” reactions overview
– Capture light energy using chlorophyll
– Split H2O to electrons, protons and oxygen
– Release O2
– Reduce NADP+ to NADPH
– Generate ATP from ADP by photophosphorylation
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• The Calvin cycle overview
- begins with carbon fixation, incorporating CO2 into organic molecules
- forms sugars from these organic molecules, using ATP and NADPH (from light reactions)
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Light
H2O
Chloroplast
LightReactions
NADP+
P
ADP
i+
Overview of Photosynthesis 1
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Light
H2O
Chloroplast
LightReactions
NADP+
P
ADP
i+
ATP
NADPH
O2
Overview of Photosynthesis 2
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Light
H2O
Chloroplast
LightReactions
NADP+
P
ADP
i+
ATP
NADPH
O2
CalvinCycle
CO2
Overview of Photosynthesis 3
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Light
H2O
Chloroplast
LightReactions
NADP+
P
ADP
i+
ATP
NADPH
O2
CalvinCycle
CO2
[CH2O]
(sugar)Overview of Photosynthesis 4
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Chlorophyll is the light-capturing substance
• Anchored to thylakoid membranes by proteins
Surrounded by other pigment
molecules, enzymes and
electron carriers
A “photosystem”
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(a) Excitation of isolated chlorophyll molecule
Heat
Excitedstate
(b) Fluorescence
Photon Groundstate
Photon(fluorescence)
En
erg
y o
f el
ectr
on
e–
Chlorophyllmolecule
If illuminated, a solution of chlorophyll will fluoresce, giving off light and heat
Illustration of important properties of chlorophyll
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PhotosyntheticEnergy Capture
THYLAKOID SPACE(INTERIOR OF THYLAKOID)
STROMA
e–
Pigments-chlorophylland accessory
Photon
Transferof energy
Special pair ofchlorophyll amolecules
Th
yla
koid
me
mb
ran
e
Photosystem
Primaryelectronacceptor
Reaction-centercomplex
Light-harvestingcomplexes
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Pigmentmolecules
Light
P680
e–
Primaryacceptor
2
1
e–
e–
2 H+
O2
+3
H2O
1/2
4
Pq
Pc
Cytochromecomplex
Electron transport chain
5
ATP
Photosystem I(PS I)
Light
Primaryacceptor
e–
P700
6
Fd
Electron transport chain
NADP+
reductase
NADP+
+ H+
NADPH
8
7
e–
e–
6
“Z-Diagram” of photosynthesis
Photosystem II(PS II)
This illustrates “non-cyclic” electron flow- electrons enter with water and leave with NADPH
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ATPPhotosystem II
Photosystem I
Primary acceptor
Pq
Cytochromecomplex
Fd
Pc
Primaryacceptor
Fd
NADP+
reductaseNADPH
NADP+
+ H+
Cyclic electron flow uses only photosystem I and
produces ATP, but not NADPH
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• “Light” reactions of PSI and PSII generate ATP and “reducing power” in the form of NADPH
• Reducing power allows the conversion of carbon dioxide to carbohydrate
• CO2 to CH2O requires NADPH reducing power
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Ribulose bisphosphate(RuBP)
3-Phosphoglycerate
Short-livedintermediate
Phase 1: Carbon fixation
(Entering oneat a time)
Rubisco
Input
CO2
P
3 6
3
3
P
PPP
ATP6
6 ADP
P P6
1,3-Bisphosphoglycerate
6
P
P6
66 NADP+
NADPH
i
Phase 2:Reduction
Glyceraldehyde-3-phosphate(G3P)
1 POutput G3P
(a sugar)
Glucose andother organiccompounds
CalvinCycle3
3 ADP
ATP
5 P
Phase 3:Regeneration ofthe CO2 acceptor(RuBP)
G3P
Carbon fixation conversion of carbon dioxide to carbohydrate
Rubisco is the key
enzyme of the cycle
Plants that use this cycle
exclusively are C3 plants
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• Dehydration is a problem for plants, sometimes requiring trade-offs with other metabolic processes, especially photosynthesis
• Plants have evolved two alternate types of carbon fixation
• C4 and Crassulean Acid Metabolism (CAM) fixation
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LightReactions:
Photosystem II Electron transport chain
Photosystem I Electron transport chain
CO2
NADP+
ADP
P i+
RuBP 3-Phosphoglycerate
CalvinCycle
G3PATP
NADPHStarch(storage)
Sucrose (export)
Chloroplast
Light
H2O
O2
C3 Photosynthesis: a review
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Note Card
What is the “reducing power” of NADPH and how does it link the light reactions with the Calvin
Cycle?