1. The Reaction of Photosynthesis Section 6.2

2. Reaction of Photosynthesis During photosynthesis (p.syn) captured solar energy is converted to chemical energy. During photosynthesis (p.syn) captured solar energy is converted to chemical energy. This chemical energy is stored in the bonds of the glucose molecule. This chemical energy is stored in the bonds of the glucose molecule.

3. Question to be Answered: How do we move from solar energy to Glucose? How do we move from solar energy to Glucose?

4. Reaction of Photosynthesis P.syn. Is not a single reaction, but a series of complex chem rxn’s. P.syn. Is not a single reaction, but a series of complex chem rxn’s.

5. Some Basics

6. ATP ATP is the molecule that provides immediate energy for cellular function. ATP is the molecule that provides immediate energy for cellular function. During photosynthesis, ATP is Formed when H+ ions escape through the ATP synthase complexes, releasing energy, and energy is used to combine ADP and Pi. (chemiosmosis) During photosynthesis, ATP is Formed when H+ ions escape through the ATP synthase complexes, releasing energy, and energy is used to combine ADP and Pi. (chemiosmosis)

7. ADP Formed by breaking one of the phosphate bonds in ATP. Formed by breaking one of the phosphate bonds in ATP.

8. ATP and ADP

9. NADP+ NADP+ accepts one hydrogen atom and 2 electrons to for NADPH at several places during photosynthesis. NADP+ accepts one hydrogen atom and 2 electrons to for NADPH at several places during photosynthesis.

10. NADPH NADPH: can donate electrons to other molecules in the cell to become NADP+ again. NADPH: can donate electrons to other molecules in the cell to become NADP+ again.

12. Photosynthesis (Big Picture) Chlorophyll in the chloroplasts absorb solar energy and convert it to chemical energy. Chlorophyll in the chloroplasts absorb solar energy and convert it to chemical energy. In this chemical form, the energy can be transported and stored. In this chemical form, the energy can be transported and stored.

13. 3 stages of Photosynthesis The Quick Version

14. Stage 1 Solar energy is captured and transferred to electrons. Solar energy is captured and transferred to electrons. Easy enough? Easy enough?

15. Stage 2 Captured solar energy is used to make ATP, and to transfer high-energy electrons to NADP+. Captured solar energy is used to make ATP, and to transfer high-energy electrons to NADP+. This yields NADPH which is used as a high energy electron carrier molecule. This yields NADPH which is used as a high energy electron carrier molecule.

16. Stages 1 & 2 Stages 1 & 2 are a series of rxn’s energized by light Stages 1 & 2 are a series of rxn’s energized by light LIGHT-DEPENDENT REACTIONS. LIGHT-DEPENDENT REACTIONS.

17. Light Dependent rxn’s Require chlorophyll, and occur on thylakoid membranes in the chloroplasts. Require chlorophyll, and occur on thylakoid membranes in the chloroplasts. Chlorophyll absorbs light-energy. Chlorophyll absorbs light-energy. This energy will “EVENTUALLY” be transferred to carbon molecules. This energy will “EVENTUALLY” be transferred to carbon molecules.

18. Stage 3 Energy stored in ATP and high-energy electrons carried by NADPH to form energy-rich organic molecules like glucose. Energy stored in ATP and high-energy electrons carried by NADPH to form energy-rich organic molecules like glucose.

19. Stage 3 (carbon fixation) Carbon from Carbon dioxide is incorporated into organic molecules like glucose. Carbon from Carbon dioxide is incorporated into organic molecules like glucose. This rxn takes place in the stoma, and uses ATP and high-energy electrons from NADPH. This rxn takes place in the stoma, and uses ATP and high-energy electrons from NADPH. Carbon fixation occurs via the Calvin Cycle (light independent rxn) Carbon fixation occurs via the Calvin Cycle (light independent rxn)

20. Photosynthesis

21. The Stages in More Detail

22. Stage 1

23. Stage 1: Capturing Solar Energy Chlorophyll and other pigments are found in clusters in the Thylakoid membrane. (photosystem) Chlorophyll and other pigments are found in clusters in the Thylakoid membrane. (photosystem) Solar energy is captured when electron in a chlorophyll molecule absorbs a photon and becomes “excited” Solar energy is captured when electron in a chlorophyll molecule absorbs a photon and becomes “excited” Photon has now been converted to chemical energy because the electron is excited. Photon has now been converted to chemical energy because the electron is excited.

24. Stage 1: Capturing Solar Energy Excited electron is then removed from photosystem and passed from one molecular complex to another via photolysis. Excited electron is then removed from photosystem and passed from one molecular complex to another via photolysis. Photolysis: energy absorbed by chlorophyll is used to split water into hydrogen ions and oxygen gas. Photolysis: energy absorbed by chlorophyll is used to split water into hydrogen ions and oxygen gas. See Figure 4 page 190. See Figure 4 page 190.

25. Stage 2

26. Stage 2: Electron Transfer and ATP Synthesis Energy now present in electrons that have been removed from water molecule. Energy now present in electrons that have been removed from water molecule. Electrons contain potential energy. Electrons contain potential energy. This potential energy will be used, and the electrons will eventually return to their original energy levels. This potential energy will be used, and the electrons will eventually return to their original energy levels. This energy is used to make ATP from ADP and Pi. This energy is used to make ATP from ADP and Pi.

27. Electron Transport Chain See figure 3 page 189 See figure 3 page 189

28. Electron Transport Chain Alberta learning Alberta learning

29. Oxidation-Reduction Reactions See Figure 3 page 189. See Figure 3 page 189. Higher-energy electron donors pass electrons to lower-energy electron acceptors. (oxidation- reduction reaction.) (redox) Higher-energy electron donors pass electrons to lower-energy electron acceptors. (oxidation- reduction reaction.) (redox) Oxidation: rxn where electrons lost. Oxidation: rxn where electrons lost. Reduction: rxn where electrons gained. Reduction: rxn where electrons gained.

30. NADPH An Electron donor. An Electron donor.

31. NADP+ Electron acceptor. Electron acceptor.

32. NADPH  NADP+ NADPH oxidized, loses H nucleus (with accompanying electrons). NADPH oxidized, loses H nucleus (with accompanying electrons). NADPH becomes NADP+. NADPH becomes NADP+. The reverse would be true as well. The reverse would be true as well. NADP+ could gain H (and electrons) to become NADPH. NADP+ could gain H (and electrons) to become NADPH.

33. Just for Fun What stage of photosynthesis are we in?? What stage of photosynthesis are we in?? Answer: Stage 2 Answer: Stage 2

34. Electron gain and Energy When an element or molecule gains electrons, it releases energy to become more stable. When an element or molecule gains electrons, it releases energy to become more stable. Therefore, when NADP+ is converted to NADPH, energy is released. Therefore, when NADP+ is converted to NADPH, energy is released.

35. This is Killer Important!! When electrons are gained: When electrons are gained: Energy is released. Energy is released. So, when NADP+ becomes NADPH, energy is released. So, when NADP+ becomes NADPH, energy is released. This allows NADPH to be able to donate electrons in the future to complete other processes. This allows NADPH to be able to donate electrons in the future to complete other processes.

36. Photosystems I & II

38. Photosystems 1 & 2 Photosystem II comes first. Photosystem II comes first. Why II? Why II? They are named in the order in which they were discovered, not their place in the photosynthetic process. They are named in the order in which they were discovered, not their place in the photosynthetic process.

39. What Happens to the Electrons Next In photosystem II, electrons are excited and lifted to the top of the energy “staircase” of the electron transport chain. In photosystem II, electrons are excited and lifted to the top of the energy “staircase” of the electron transport chain. At each step, energy is lost. At each step, energy is lost. As they move down toward the bottom of the energy staircase, they migrate toward the thylakoid Lumen. (inside of thylakoid) As they move down toward the bottom of the energy staircase, they migrate toward the thylakoid Lumen. (inside of thylakoid) Releasing energy, and pulling hydrogen ions across membrane and into the lumen. Releasing energy, and pulling hydrogen ions across membrane and into the lumen.

40. Electrons Out of energy, they are passed to Photosystem I. Out of energy, they are passed to Photosystem I. These electrons replace electrons that have been excited by light in photosystem I. These electrons replace electrons that have been excited by light in photosystem I. Energized electrons in photosystem I are transferred to NADP+. Energized electrons in photosystem I are transferred to NADP+. NADPH is created, and can transfer high-energy electrons to the Calvin Cycle in step 3. NADPH is created, and can transfer high-energy electrons to the Calvin Cycle in step 3.

42. Chemiosmosis H+ ions in Lumen create a concentration gradient. H+ ions in Lumen create a concentration gradient. H+ ions can only exit through the ATP synthase complex embedded in the thylakoid membrane. H+ ions can only exit through the ATP synthase complex embedded in the thylakoid membrane. As the H+ ions exit, energy is released. As the H+ ions exit, energy is released. The ATP synthase complex uses ADP and Pi to create ATP. The ATP synthase complex uses ADP and Pi to create ATP. This process: Chemiosmosis. This process: Chemiosmosis.

43. Summary of Light Dependent Reactions 1. Electrons from photosystem II are transferred along an electron transport chain and across the thylakoid membrane into the lumen. 1. Electrons from photosystem II are transferred along an electron transport chain and across the thylakoid membrane into the lumen. 2. Some of their energy pulls H+ ions across the membrane, yielding positive charge in the lumen 2. Some of their energy pulls H+ ions across the membrane, yielding positive charge in the lumen 3. Electrons low on energy are transferred to photosystem I, and absorb solar energy. 3. Electrons low on energy are transferred to photosystem I, and absorb solar energy. 4. High-energy electrons from Photosystem I are transferred to NADP+ to form NADPH. 4. High-energy electrons from Photosystem I are transferred to NADP+ to form NADPH. 5. Energy released by exit of H+ ions used to create ATP. 5. Energy released by exit of H+ ions used to create ATP.

44. Stage 3

45. Up until this point, we have been dealing with light dependent reactions. Up until this point, we have been dealing with light dependent reactions. Stage 3 will take the products of stages 1 and 2, and finish the construction of glucose. Stage 3 will take the products of stages 1 and 2, and finish the construction of glucose.

46. Carbon Fixation Formation of high-energy organic molecules from carbon dioxide. Formation of high-energy organic molecules from carbon dioxide.

47. The Calvin Cycle Utilizes ATP and high-energy electrons carried by NADPH to make G3P. Utilizes ATP and high-energy electrons carried by NADPH to make G3P. G3P is a sugar used to create glucose. G3P is a sugar used to create glucose.

48. Calvin Cycle

49. Where did the ATP and the NADPH come from? Stages 1 and 2

50. Where did the carbon dioxide come from? Diffuses directly into leaf.