1. BIOL 205 :: Photosynthesis Lecture 1 Introduction and the light reactions

2. What is photosynthesis? The process of converting solar energy into chemical energy. Can use only water and carbon dioxide to create sugars = chemical energy. Responsible for removal of ~ 200 billion tons of C from the atmosphere yearly.

3. What is photosynthesis? 6CO 2 + 12 H 2 O + hv C 6 H 12 O 6 +6O 2 +6H 2 O hv designates light you should memorize this equation!! you will see it again O 2 = oxygenic photosynthesis

4. What is photosynthesis? 2 stages of photosynthesis –Light reactions and Dark reactions Light reactions convert sunlight into chemical energy (ATP + NADPH) Dark reactions use those products to form sugars (stored chemical energy)

5. Overview of Photosynthesis Light Reactions H 2 O + CO 2 NADPH ATP Dark Reactions CO 2 Sugars O2O2

6. Where does photosynthesis take place? Prokaryotes Prokaryotes have both anoxygenic and oxygenic Cyanobacteria have oxygenic -Photosynthesis on thylakoids (from plasma membrane) -Cyanobacteria are source of eukaryotic photosynthesis Eukaryotes Oxygenic only Takes place in chloroplasts

7. Chloroplast Morphology

8. Chloroplast Morphology-Terms Inner Membrane Outer Membrane Thylakoid Thylakoid lumen Stroma Granum

9. How can light provide energy for plants? Light is composed of particles: photons Light behaves like a wave –Can e described w/ wavelength & frequency Only a small portion of the electromagnetic spectrum.

10. The electromagnetic spectrum PAR = photosynthetically available radiation

11. Pigments Pigment = a light absorbing molecule Associated with the thylakoid membranes Chlorophyll –Chl a and Chl b (Chl c in some algae) Xanthophylls Carotenoids –ß-carotene

12. Chlorophyll Chl a has a methyl group Chl b has a carbonyl group Porphyrin ring delocalized e- Phytol tail

13. Different pigments absorb light differently

15. 2-minute quiz 1. What is the relationship between the structure of chlorophyll and its location in the chloroplast? 2. Why are plants green?

16. Light Reactions 1: Light capture and redox 2 spatially & functionally distinct units = Photosystems Photosystem II = 1st stage Photosystem I = 2nd stage Named after order of discovery

17. Light capture 1 LHC Reaction Center 1. Most Chlorophyll is located in the Light Harvesting Complex 2. Sunlight is absorbed in the LHC and is passed from pigment to pigment Remember the porphyrin ring? ß-carotene Chl b Chl a

18. Light capture - 2 LHC Reaction Center P680 chlorophylls * 3. Energy finally ends up in a pair of special chlorophyll a molecules: P680 4. e- in P680 Chl a goes to excited state and is shed = Charge separation e-*e-* Optimal @ <680 nm

19. Light capture - 3 LHC Reaction Center + e-*e-* Q 5. High-energy e- accepted by quinone Q = primary e- acceptor 6. Q has been reduced; P680 Chl a has been oxidized Oxidation by light = photo-oxidation e- transport chain 7. The excited e- is shunted into the electron transport chain

20. Light capture - 4 H2OH2O 1/2 O 2 4H + O 2 evolving complex 8. The O 2 evolving complex + Chl a+ strip e- from H 2 O and reduce Chl a+ Chl a+ = most powerful biological oxidizing agent e- +

21. Light capture - 5 9. The reaction center is reset and ready to go again

22. Light Capture Movie

23. PSII electron transport chain Q e- H+ 1. Q accepts 2 e- from P680 and removes 2 H+ from the stroma 2. Q passes the e- to cytochrome b/f complex & pumps the 2H+ into thylakoid lumen b/f cytochrome complex e- 3. As the e- moves through b/f more H+ are pumped into lumen

24. The PS II Electron transport chain Q e- H+ 2H+ b/f cytochrome H+ complex plastocyanin e-

25. PS II to PS I plastocyanin e- 4. e- end up on plastocyanin: a soluble electron carrier in the lumen plastocyanin e- 5. Plastocyanin serves as e- donor for PSI reaction center Chl a

26. Photosystem I P700 e-* + plastocyanin e- 1. Charge separation and photo-oxidation are similar to PSII Optimal wavelength = 700nm 2. Plastocyanin acts as reducing agent on P700 Chl a

27. PSI electron transport chain e- Ferredoxin Fe/S 1. Ferredoxin recieves e- from P700* FAD NADP+ FAD-NAPD Reductase H+ e- 2. e- moves throuh FAD (flavin adenine dinucleotide) 3. e- plus stromal H+ are used to reduce NADP+ to NADPH NADPH = FINAL PRODUCT!

28. PSI electron transport chain e- Ferredoxin Fe/S FAD NADP+ FAD-NAPD Reductase H+ NADPH e-

29. ATP synthesis stroma lumen H+ 1. O2 evolving complex liberates H+ into lumen from water 2. Q and Cyt b/f pump H+ from stroma into lumen. 3. NADP+ scavenges protons from the stroma pH separation across membrane = Proton Motive Force!

30. ATP synthesis stroma lumen H+ F 0 F 1 complex H+ ADP + Pi ATP The energy released as protons travel down their concentration gradient is used to fuel an ATP synthase

31. Light Reactions Products In: CO2, H2O, sunlight Out: O2, ATP, NADPH