1. Generating Chemical Energy
Brought to you by
Photosynthesis

2. (INTERIOR OF THYLAKOID)
Photosystems
In the thylakoid membrane
Composed of
Reaction-center complex
Proteins w/ chlorophyll a
Light-harvesting complex
Protein w/ chlorophyll a, b and carotenoids
act as light-gathering “antenna complex”
Primary election
acceptor
Photon
Thylakoid
Light-harvesting
complexes
Reaction
center
Photosystem
STROMA
Thylakoid membrane
Transfer
of energy
Special
chlorophyll a
molecules
Pigment
THYLAKOID SPACE
(INTERIOR OF THYLAKOID)
Figure 10.12 e–

3. Photosystems
Light-harvesting complex direct NRG of photons to reaction center
Reaction-center absorbs energy:
Special chlorophyll a molecule donates e- instead of letting it fall back to ground state.
e- gets bumped up to a primary electron acceptor
REDOX
This is first step of light reactions

5. Different types Photosystems I and II PSII PSI
Named by discovery not sequence
PSII works first then PSI
PSII
reaction center chlorophyll a absorbs 680 nm.
PSI
reaction center chlorophyll a absorbs 700nm
Work together to generate ATP and NADPH
6 steps

6. Chemical NRG Production
Step 1
Photon excites p680 chlorophyll and donates e- to primary electron acceptor
REDOX
P680  p e-
Problem can this process occur twice? Why?

7. Chemical NRG Production
Step 2
H2O split
H2O  2H+ + 2e- + O
2H+ donated to thylakoid space for ETC
Oxygen kicked out
And …
Answer to original problem
e- fed to oxidized p680+ chlorophyll
Reduces back to p680, ready to do it again

8. Chemical NRG Production
Step 3
Excited e- passed from primary acceptor to PS I by ETC

9. Electron Transport Chain
Use gradient of H+ ions to rotate ATP synthesis and crush ADP to Pi (inorganic phosphate)

10. Chemical NRG Production
Step 4
Energetically “falling” e- supply NRG to H+ pump
Electrochemical gradient produced
Chemiosmosis generates ATP by synthase protein

11. Chemical NRG Production
Step 5
PS I looses e- to primary acceptor by photon excitement (same as step 1 but in PS I)
e- from ETC reaches PS I and donates to now oxidized p700+

12. Chemical NRG Production
Step 6
Excited e- passed to 2nd ETC
No H+ pumps just REDOX
Passed to NADP+ reductase and reduces NADP+ to NADPH (NADP+ + 2e-  NADPH

13. Figure 10.14 NADPH e– Mill makes ATP Photon Photosystem II

14. Still with me?? Light is used to generate NADPH and ATP
Key to this is the flow of excited electrons
Redox reactions!!
2 possible routes
Cyclic
Noncyclic
Usually used

15. Cyclic / linear flow Produces NADPH, ATP, and oxygen
Photosystem II (P680) to primary acceptor
Through an E-T.C. to Photosystem I
ATP produced
Noncyclic photophosphorylation
P700 to primary acceptor
Through 2nd E-T.C. to NADP+
NADPH

16. Figure 10.14 NADPH e– Mill makes ATP Photon Photosystem II

17. Cyclic Electron Flow Photosystem I used, not Photosystem II
Chlorophyll a is recycled back down to its ground state
Photon hits P700 (PS I), excites e- passing it to primary electron receptor
e- don’t go to NADP+ reductase
Enter into electron chain
return to P700 to complete the cycle
Produces ATP, not O2 or NADPH

18. Primary Fd acceptor Pq NADP+ reductase Cytochrome NADPH complex Pc
ATP
Figure 10.15
Photosystem II
Photosystem I

19. Why is a Cyclic form needed?
Noncyclic e- flow produces ATP and NADPH in = equal quantities
Calvin Cycle uses more ATP than NADPH
Does it make sense now?
Cyclic electron flow makes ATP only
The concentration of NADPH regulate path
Reduce all NADP+ non cyclic flow shuts down
No where for e- to flow but back to ETC

20. Quick Summary:
Goal: Light reactions use _________ power to generate _________ and _______ which provide chemical energy and reducing power to the Calvin Cycle.
The Calvin Cycle makes _____________.
Noncyclic photophosphorylation
Photosystem(s) used:
What are the products:
Cyclic photophosphorylation

21. STOP

22. A Comparison of Chemiosmosis in Chloroplasts and Mitochondria
Chemiosomosis:
An nrg coupling mechanism that uses nrg stored in a H+ gradient across a membrane to drive cellular work (ATP synthesis)
Chloroplasts and mitochondria generate ATP this way
In both organelles, an electron transport chain pumps protons across a membrane as electrons are passed along a series of increasingly electronegative carriers.
This transforms redox energy to a proton-motive force in the form of an H+ gradient across the membrane.
ATP synthase molecules harness the proton-motive force to generate ATP as H+ diffuses back across the membrane.

23. Difference: What form does the energy come from in:
Cellular Respiration?
Photosynthesis
Key
Higher [H+]
Lower [H+]
Mitochondrion
Chloroplast
MITOCHONDRION
STRUCTURE
Intermembrance
space
Membrance
Matrix
Electron
transport
chain H+
Diffusion
Thylakoid
Stroma
ATP P
ADP+
Synthase
CHLOROPLAST
Figure 10.16