Overview of Photosynthesis
importance: fix tons of CO2 per year, used as energy for virtually all organisms
similarity to ETC/ox-phos, PPP and tied to gng
2 phaseslight-dependent rxns (light rxns)light-independent rxns (dark rxns)
location: chloroplast
Detailed Chloroplast Structure
• Porous outer membrane, tight inner membrane
• Stroma• thylakoid disk• granum (grana)• thylakoid lumen• Light rxns take place on
thylakoid membrane, dark rxns stroma
Light is Captured by Several Classes of Molecules
Fig. 19-40(a) Lehninger POB 4th Ed.
Chlorophylls
Light is Captured by Several Classes of Molecules
Fig. 19-40 (b)-(d) Lehninger POB 4th Ed.
Carotenoids and other conjugated compounds
Light ReactionsFig. 19-41 Lehninger POB 4th Ed.
Reason for numerous molecules
Light ReactionsFig. 19-45 Lehninger POB 4th Ed.
“Special Pair”
Photosystems I and II
Photosystem I (P700) Fig. 19-49 Lehninger POB 4th Ed.
Not confident all molecules have been ID’d
Major molecules
Some of the reactions which occur
NADPH produced
Photosystem II (P680) Fig. 19-49 Lehninger POB 4th Ed.
Major molecules
ATP produced
PSI and PSII Together Formthe “Z-scheme”
PhotophosphorylationFig. 19-54(c) Lehninger POB 4th Ed.
Proton gradient develops as e– are transported
high pH inside thylakoid lumen
Water Splitting Complex Science 292:447, 2001
• PSII does not directly perform sequential one-e– transfers• Rather, it has an integral inorganic catalyst from which it
extracts 4 e– and then reacts with 2 H2Os to form O2
• 4 Mn electronically coupled as Mn4 cluster
Photophosphorylation
Proton gradient develops as e– are transported
high pH inside thylakoid lumen
protons come out through Fo of “C-ATPase” (CFo)
F1 rotor forms ATP (CF1)
Cyclic PhotophosphorylationFig. 19-49 Lehninger POB 4th Ed.
P700 only
NO NADPH produced, only ATP (less)
Major molecules: P700, Fd, Cyt. B6, Cyt f, PC
~Idealized Balanced Net Rxn
"8" h2 H2O O2
~3 ADP+ ~3 Pi
~3 ATP
2 NADP+2 NADPH
+ 2 H+
Dark Reactions - C3 plants
3PG first molecule produced containing the fixed carbon
Dark Reactions - C3 plants
3PG first molecule produced containing the fixed carbon
Dark Reactions - C3 plants
3PG first molecule produced containing the fixed carbon
Dark Reactions – Rubisco Reaction
rubisco is the most abundant protein in the world
CH
C
C
OH
CH2OPO32-
OH
CH2OPO32-
O
H
C OH
CO2
CH2OPO32-
H2
CO2
rubisco
3PG Glucose
• What rxns are required?
Syphoned offContinues through pathway
12 3-PG 12 1,3-bisPG 12 Glyceraldehyde-3-PPG Kinase
12 ATP 12 ADP
GAPDH
12 NADPH
+ 12 H+12 NADP+
+ 12 Pi
5 DHAP3 2
3 Fru-1,6-P2 3 Fru-6-P2
1 Glc-6-P 1 Glc12 Glyceraldehyde-3-P4 3
Aldolase
TPI
PGmutase
H2O Pi
FBPase
H2O Pi
G6Pase
Regeneration ofRibulose-1,5-bisphosphate
2 F-6-P+
2 G-3-P
2 Ribul-5-P 2 Ribul-1,5-P2
Isomerase Kinase
2 Sed-1,7-P2 2 Sed-7-P
Transketolase
Phosphatase
H2O Pi
2 Gly-3-P
Transketolase
2 Xyl-5-P+
2 Ery-4-PTransaldolase 2 DHAP
Ribul-5-P 2 Xylul-5-PRibul-1,5-P2
IsomeraseKinaseRibul-5-P
Ribul-1,5-P2
Kinase
~Idealized Balanced Net Rxn
"8" h + 2 H2O + ~3 ADP + ~3 Pi + 2 NADP+ O2 + ~3 ATP + 2 H+ + 2 NADPH
Light-dependent Reactions
Light-independent Reactions
6 CO2 + 18 ATP + 12 NADPH + 12 H+ 1 Glc + 18 ADP + 18 Pi + 12 NADP+
C4 PlantsThe Hatch-Slack Pathway
Fig. 20-23 Lehninger POB 4th Ed.
• Molecular logic• Division of labor• Additional Reactions
Additional Rxns of the Hatch-Slack Pathway
Fig. 20-23 Lehninger POB 4th Ed.
Regulation Occurs Several WaysFig. 20-18 Lehninger POB 4th Ed.
1. Regulation by lighta. FBPase activatedb. light-induced Mg2+ efflux to stromac. thioredoxin
2. Rubisco Allosterism(a) carbamoylation stim(b) rib-1,5-P2 inh. Carb.(c) B overcome ATP?(d) 2-carboxyarabinitol-1-
phosphate
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