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