Overview of Photosynthesis

1
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 phases
• light-dependent rxns (light rxns)
• light-independent rxns (dark rxns)
• location chloroplast

2
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

3
Light is Captured by Several Classes of
MoleculesFig. 19-40(a) Lehninger POB 4th Ed.

• Chlorophylls

4
Light is Captured by Several Classes of
MoleculesFig. 19-40 (b)-(d) Lehninger POB 4th Ed.

• Carotenoids and other conjugated compounds

5
Light ReactionsFig. 19-41 Lehninger POB 4th Ed.

• Reason for numerous molecules

6
Light ReactionsFig. 19-45 Lehninger POB 4th Ed.

• Special Pair
• Photosystems I and II

7
Photosystem I (P700) Fig. 19-49 Lehninger POB
4th Ed.

• Not confident all molecules have been IDd
• Major molecules
• Some of the reactions which occur
• NADPH produced

8
Photosystem II (P680) Fig. 19-49 Lehninger POB
4th Ed.

• Major molecules
• ATP produced

9
PSI and PSII Together Formthe Z-scheme
10
PhotophosphorylationFig. 19-54(c) Lehninger POB
4th Ed.

• Proton gradient develops as e are transported
• high pH inside thylakoid lumen

11
Water Splitting Complex Science 292447, 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

12
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)

13
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

14
Idealized Balanced Net Rxn
15
Dark Reactions - C3 plants

• 3PG first molecule produced containing the fixed
  carbon

16
Dark Reactions - C3 plants

• 3PG first molecule produced containing the fixed
  carbon

17
Dark Reactions - C3 plants

• 3PG first molecule produced containing the fixed
  carbon

18
Dark Reactions Rubisco Reaction

• rubisco is the most abundant protein in the world

19
3PG ? Glucose

• What rxns are required?

20
Regeneration ofRibulose-1,5-bisphosphate
21
Idealized Balanced Net Rxn
22
C4 PlantsThe Hatch-Slack PathwayFig. 20-23
Lehninger POB 4th Ed.

• Molecular logic
• Division of labor

• Additional Reactions

23
Additional Rxns of the Hatch-Slack PathwayFig.
20-23 Lehninger POB 4th Ed.
24
Regulation Occurs Several WaysFig. 20-18
Lehninger POB 4th Ed.

• Regulation by light
• a. FBPase activated
• b. light-induced Mg2 efflux to stroma
• c. thioredoxin
• 2. Rubisco Allosterism
• (a) carbamoylation stim
• (b) rib-1,5-P2 inh. Carb.
• (c) B overcome ATP?
• (d) 2-carboxyarabinitol-1-phosphate