1. Biochem 3070 - Photosynthesis PHOTOSYNTHESIS In 1780 Joseph Priestly discovered photosynthesis: “…plants can “restore air which has been injured by the burning of candles.” “…the air would neither extinguish a candle, nor was it all inconvenient to a mouse which I put into it.” Stryer, Biochemistry, 4 th ed.

2. Biochem 3070 - Photosynthesis Photosynthesis provides essentially all free energy in biological systems by converting solar energy into chemical energy. Carbohydrates are formed from light- driven reactions that collectively appear deceptively simple: CO 2 + H 2 O + light  C n H 2n O n + O 2

3. Biochem 3070 - Photosynthesis Photosynthesis occurs in specialized organelles called chloroplasts: Stryer, et.al., Biochemistry, 5 th ed.

4. Biochem 3070 - Photosynthesis TEM of Chloroplast from Corn Biochemistry, Voet & Voet,, 3rd Ed

5. Biochem 3070 - Photosynthesis Stryer, et.al., Biochemistry, 5 th ed.

6. Biochem 3070 - Photosynthesis Photosynthesis consists of two sets of reactions: the LIGHT and DARK reactions. The LIGHT-driven reactions are the primary events of photosynthesis; these occur in the thylakoid membrane. The DARK reactions occur in the stroma.

7. Biochem 3070 - Photosynthesis The light-reactions of photosynthesis generate high-energy electrons that are used to form NADPH. On their way to NADPH, these high- energy electrons flow through a membrane-bound “electron transport” pathway, generating a proton motive potential (Δp) from which ATP is made.

8. Biochem 3070 - Photosynthesis Stryer, et.al., Biochemistry, 5 th ed.

9. Biochem 3070 - Photosynthesis

10. Walker, et.al, Fundamentals of Chemistry, 1st ed.

11. Biochem 3070 - Photosynthesis Chlorophyll a: Stryer, et.al., Biochemistry, 5 th ed.

12. Biochem 3070 - Photosynthesis

13. Sunlight spectrum, Chlorophyll a and Bacteriochlorophyll a

14. Biochem 3070 - Photosynthesis Voet & Voet, Biochemistry, 3 rd ed., pg 875

15. Biochem 3070 - Photosynthesis Light-harvesting Pigments help absorb wavelengths of light in the region of the spectrum where chlorophyll pigments do not absorb light. Photons absorbed by these pigments also transfer energy to chlorophyll. β-carotene helps protect plants from photochemical reactions, expecially those involving oxygen; (it serves as an “antioxidant.”)

16. Biochem 3070 - Photosynthesis

17. The majority of chlorophyll molecules in a photosynthetic unit do not get involved in photosynthesis directly. Rather, they transfer their absorbed energy to a reaction center complex. C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C

18. Biochem 3070 - Photosynthesis Light energy absorbed by antenna chlorophyll molecules and auxillary pigments is transferred to specialized reaction centers. This energy transfer (often called “resonance energy transfer” or “exciton hopping”) is very efficient, approaching 100%!

19. Biochem 3070 - Photosynthesis Stryer, et.al., Biochemistry, 5 th ed.

20. Biochem 3070 - Photosynthesis Voet & Voet, Biochemistry, 3 rd ed., pg 877

21. Biochem 3070 - Photosynthesis Stryer, et.al., Biochemistry, 5 th ed.

22. Biochem 3070 - Photosynthesis Voet & Voet, Biochemistry, 3 rd ed., pg 877

23. Biochem 3070 - Photosynthesis Voet & Voet, Biochemistry, 3 rd ed., pg 877

24. Biochem 3070 - Photosynthesis Garrett & Grisham, Biochemistry, 3 rd ed.

25. Biochem 3070 - Photosynthesis Stryer, et.al., Biochemistry, 5 th ed.

26. Biochem 3070 - Photosynthesis X-ray Structure of Photosystem II (S. elongatus) Stryer, et.al., Biochemistry, 5 th ed.

27. Biochem 3070 - Photosynthesis Voet & Voet, Biochemistry, 3 rd ed., pg 888 X-ray Structure of Photosystem II (S. elongatus)

28. Biochem 3070 - Photosynthesis Mn cluster in the OEC Schematic mechanism of oxygen generation in PSII: Voet & Voet, Biochemistry, 3 rd ed., pg 889

29. Biochem 3070 - Photosynthesis Stryer, et.al., Biochemistry, 5 th ed.

30. Biochem 3070 - Photosynthesis Voet & Voet, Biochemistry, 3 rd ed., pg 877

31. Biochem 3070 - Photosynthesis Stryer, et.al., Biochemistry, 5 th ed.

32. Biochem 3070 - Photosynthesis Herbicides that inhibit Photosystem II by blocking the transfer of electrons to QH 2 : Stryer, et.al., Biochemistry, 5 th ed.

33. Biochem 3070 - Photosynthesis Voet & Voet, Biochemistry, 3 rd ed., pg 877

34. Biochem 3070 - Photosynthesis Electron Flow through PSII:Electron Flow through Cytochrome bf: Plastocyanin: Stryer, et.al., Biochemistry, 5 th ed.

35. Biochem 3070 - Photosynthesis Photosystem I: Stryer, et.al., Biochemistry, 5 th ed.

36. Biochem 3070 - Photosynthesis Photosystem I: 700nm photon Stryer, et.al., Biochemistry, 5 th ed.

37. Biochem 3070 - Photosynthesis Ferredoxin Structure Stryer, et.al., Biochemistry, 5 th ed.

38. Biochem 3070 - Photosynthesis “Z-Scheme” of Photosynthesis: Stryer, et.al., Biochemistry, 5 th ed.

39. Biochem 3070 - Photosynthesis Stryer, et.al., Biochemistry, 5 th ed.

40. Biochem 3070 - Photosynthesis Stryer, et.al., Biochemistry, 5 th ed.

41. Biochem 3070 - Photosynthesis Stryer, et.al., Biochemistry, 5 th ed.

42. Biochem 3070 - Photosynthesis Stryer, et.al., Biochemistry, 5 th ed. Andre Jagendorf and Ernest Uribe’s classic experiment, showing the production of ATP from an artificially induced proton gradient across isolated chloroplasts in the absence of any light! (First Reported in 1965)

43. Biochem 3070 - Photosynthesis

44. Stroma Lumen (Thylakoid Space)

45. Biochem 3070 - Photosynthesis Stroma Lumen Inner-membrane Space Matrix Stryer, et.al., Biochemistry, 5 th ed.

46. Biochem 3070 - Photosynthesis What about CO 2 ? CO 2 + H 2 O + light  C n H 2n O n + O 2

47. Biochem 3070 - Photosynthesis Melvin Calvin discovered the CO 2 acceptor by using C-14 radioactive labeled carbon dioxide: He discovered that the reactions of CO 2 fixation are almost identical to reactions of the phosphate shunt: Stryer, et.al., Biochemistry, 5 th ed.

48. Biochem 3070 - Photosynthesis The Calvin Cycle: From light-driven reactions Stryer, et.al., Biochemistry, 5 th ed.

49. Biochem 3070 - Photosynthesis Ribulose 1,5-bisphosphate carboxylase/oxygenase [“rubisco”]: Rubisco consitutes more than 16% of all protein in chloroplasts. It is the most abundant protein in the entire biosphere! Stryer, et.al., Biochemistry, 5 th ed.

50. Biochem 3070 - Photosynthesis Proposed mechanism for Rubisco: Stryer, et.al., Biochemistry, 5 th ed.

51. End of Slides For Photosynthesis Credits: Many of the diagrams used in these slides were taken from Stryer, et.al, Biochemistry, 5th Ed., Freeman Press (in our course textbook) and from prior editions of this text.