1. Ch 10 Photosynthesis--> To make with light!

2. LE 10-2 Plants Unicellular protist Multicellular algae Cyanobacteria Purple sulfur bacteria 10 µm 1.5 µm 40 µm Photoautotrophs: Self feeders, producers Use light and inorganic molecules to make own organic molecules.

3. Heterotrophs (food from others) : -Consumers -Obtain organic material from other organisms -Dependent on photoautotrophs for food and oxygen

4. Photosynthesis: conversion of light energy into chemical energy Simplified rxn: 6CO 2 + 6H 2 O + light --> C 6 H 12 O 6 + 6O 2 Reaction: 6CO 2 + 12H 2 O + light --> C 6 H 12 O 6 + 6O 2 + 6H 2 O glucose Simplest rxn: CO 2 + H 2 O + light --> [CH 2 O] + O 2 carbohydrate

5. LE 10-3 Leaf cross section Vein Mesophyll Stomata CO 2 O2O2 Mesophyll cell Chloroplast 5 µm Outer membrane Intermembrane space Inner membrane Thylakoid space Thylakoid GranumStroma 1 µm 6CO 2 + 6H 2 O + light --> C 6 H 12 O 6 + 6O 2 Gas enters through stomata Enters through roots Exits through stomata or used in respiration Organic molecule for fuel or other

6. Two major reactions in photosynthesis Light-dependent (in thylakoid) Light-independent aka dark or Calvin cycle (in stroma)

7. LE 10-7 Chloroplast Light Reflected light Absorbed light Transmitted light Granum Stroma Chlorophyll in thylakoid membranes

8. LE 10-10 CH 3 CHO in chlorophyll a in chlorophyll b Porphyrin ring: light-absorbing “head” of molecule; note magnesium atom at center Hydrocarbon tail: interacts with hydrophobic regions of proteins inside thylakoid membranes of chloroplasts; H atoms not shown

9. LE 10-9a Chlorophyll a Chlorophyll b Carotenoids Wavelength of light (nm) Absorption spectra Absorption of light by chloroplast pigments 400 500600 700

10. How do we know that absorption of certain wavelengths of light by plants stimulates a chemical reaction in plants? Specifically how do we know that O 2 is a product?

11. LE 10-9c Engelmann’s experiment (1883): Action spectrum 400 500 600 700 Aerobic bacteria Filament of algae What would be an important control experiment?

12. Chlorophyll a: –main photosynthetic pigment Accessory pigments –chlorophyll b and carotenoids absorb excessive light that would damage chlorophyll –broaden the spectrum used for photosynthesis

13. When a pigment absorbs light –departs from a ground state to an excited state --> unstable Draw –excited electrons fall back to the ground state, give off photons (glow)-->fluorescence Light-Induced Excitation:

14. LE 10-11 Excited state Heat Photon (fluorescence) Ground state Chlorophyll molecule Photon Excitation of isolated chlorophyll molecule Fluorescence Energy of electron e–e–

15. LE 10-5_1 H2OH2O LIGHT REACTIONS Chloroplast Light Light-dependent rxn: in thylakoid

16. LE 10-5_2 H2OH2O LIGHT REACTIONS Chloroplast Light ATP NADPH O2O2

17. LE 10-5_3 H2OH2O LIGHT REACTIONS Chloroplast Light ATP NADPH O2O2 NADP + CO 2 ADP P + i CALVIN CYCLE [CH 2 O] (sugar) Calvin cycle: in stroma

18. Photosynthesis as a Redox Process Water is oxidized (e- are removed). Carbon dioxide is reduced (e- are gained).

19. Two major reactions in photosynthesis Light dependent (in thylakoid): Creates ATP and an electron carrier, NADPH Electrons supplied through splitting and oxidation of H 2 O Light -independent (aka dark or Calvin cycle)(in stroma): Synthesis of organic molecules from CO 2 Reduction reactions Endergonic: requires ATP

20. Light Reaction: Consists of 2 photosystems Occurs at two different reaction centers each surrounded by light harvesting complexes Light harvesting complex funnels energy to reaction center

21. LE 10-12 Thylakoid Photon Light-harvesting complexes Photosystem Reaction center STROMA Primary electron acceptor e–e– Transfer of energy Special chlorophyll a molecules Pigment molecules THYLAKOID SPACE (INTERIOR OF THYLAKOID) Thylakoid membrane

22. LE 10-13_1 Light P680 e–e– Photosystem II (PS II) Primary acceptor [CH 2 O] (sugar) NADPH ATP ADP CALVIN CYCLE LIGHT REACTIONS NADP + Light H2OH2O CO 2 Energy of electrons O2O2 Once P680 is oxidized (gives up e-), is it functional? How is it restored to functionality?

23. LE 10-13_2 Light P680 e–e– Photosystem II (PS II) Primary acceptor [CH 2 O] (sugar) NADPH ATP ADP CALVIN CYCLE LIGHT REACTIONS NADP + Light H2OH2O CO 2 Energy of electrons O2O2 e–e– e–e– + 2 H + H2OH2O O2O2 1/21/2 Splitting of H 2 O yields e- that fill e-”hole” in oxidized P680

24. LE 10-13_3 Light P680 e–e– Photosystem II (PS II) Primary acceptor [CH 2 O] (sugar) NADPH ATP ADP CALVIN CYCLE LIGHT REACTIONS NADP + Light H2OH2O CO 2 Energy of electrons O2O2 e–e– e–e– + 2 H + H2OH2O O2O2 1/21/2 Pq Cytochrome complex Electron transport chain Pc ATP

25. LE 10-13_4 Light P680 e–e– Photosystem II (PS II) Primary acceptor [CH 2 O] (sugar) NADPH ATP ADP CALVIN CYCLE LIGHT REACTIONS NADP + Light H2OH2O CO 2 Energy of electrons O2O2 e–e– e–e– + 2 H + H2OH2O O2O2 1/21/2 Pq Cytochrome complex Electron transport chain Pc ATP P700 e–e– Primary acceptor Photosystem I (PS I) Light

26. LE 10-13_5 Light P680 e–e– Photosystem II (PS II) Primary acceptor [CH 2 O] (sugar) NADPH ATP ADP CALVIN CYCLE LIGHT REACTIONS NADP + Light H2OH2O CO 2 Energy of electrons O2O2 e–e– e–e– + 2 H + H2OH2O O2O2 1/21/2 Pq Cytochrome complex Electron transport chain Pc ATP P700 e–e– Primary acceptor Photosystem I (PS I) e–e– e–e– Electron Transport chain NADP + reductase Fd NADP + NADPH + H + + 2 H + Light

27. After P700 is oxidized by light energy in PS I are its missing electrons replaced? If so what is the electron source? What would be the effect on photosynthesis if P700 were not reduced to its original state i.e. if the e- hole were not filled?

28. Electron Flow Noncyclic electron flow –involves both photosystems (II & I) –produces ATP and NADPH

29. LE 10-14 ATP Photosystem II e–e– e–e– e–e– e–e– Mill makes ATP e–e– e–e– e–e– Photon Photosystem I Photon NADPH

30. Cyclic Electron Flow - Uses only photosystem I - Produces only ATP, no NADPH - Generates surplus ATP –to satisfy demand in the Calvin cycle

31. LE 10-15 Photosystem I Photosystem II ATP Pc Fd Cytochrome complex Pq Primary acceptor Fd NADP + reductase NADP + NADPH Primary acceptor

32. How is ATP made? By chemiosmosis

33. LE 10-17 STROMA (Low H + concentration) Light Photosystem II Cytochrome complex 2 H + Light Photosystem I NADP + reductase Fd Pc Pq H2OH2O O2O2 +2 H + 1/21/2 2 H + NADP + + 2H + + H + NADPH To Calvin cycle THYLAKOID SPACE (High H + concentration) STROMA (Low H + concentration) Thylakoid membrane ATP synthase ATP ADP + P H+H+ i [CH 2 O] (sugar) O2O2 NADPH ATP ADP NADP + CO 2 H2OH2O LIGHT REACTIONS CALVIN CYCLE Light

34. Current chemiosmotic model: –H+ (protons) accumulate in thylakoid space 1. Through splitting of water 2. By translocation into thylakoid when e- are transported 3. By removal of H+ from stroma due to bonding with NADPH – H + diffuses from thylakoid space --> stroma through membrane enzyme, ATP synthase – Movement activates ATP synthase – ATP synthesized on stromal face where the Calvin cycle takes place

35. Products from light reactions power Calvin cycle! What are the light reaction products? ATP: energy carrier NADPH: electron carrier What is the product of the Calvin cycle? Glucose (fuel) What additional molecule must enter the Calvin cycle to make sugar? CO 2

36. Calvin cycle –Three phases: Carbon fixation (catalyzed by rubisco) Reduction Regeneration of the CO 2 acceptor (RuBP)

37. LE 10-18_1 [CH 2 O] (sugar) O2O2 NADPH ATP ADP NADP + CO 2 H2OH2O LIGHT REACTIONS CALVIN CYCLE Light Input 3 CO 2 (Entering one at a time) Rubisco 3 P P Short-lived intermediate Phase 1: Carbon fixation 6 P 3-Phosphoglycerate 6 ATP 6 ADP CALVIN CYCLE 3 P P Ribulose bisphosphate (RuBP)

38. LE 10-18_2 [CH 2 O] (sugar) O2O2 NADPH ATP ADP NADP + CO 2 H2OH2O LIGHT REACTIONS CALVIN CYCLE Light Input CO 2 (Entering one at a time) Rubisco 3PP Short-lived intermediate Phase 1: Carbon fixation 6 P 3-Phosphoglycerate 6 ATP 6 ADP CALVIN CYCLE 3 PP Ribulose bisphosphate (RuBP) 3 6 NADP + 6 6 NADPH P i 6P 1,3-Bisphosphoglycerate P 6 P Glyceraldehyde-3-phosphate (G3P) P1 G3P (a sugar) Output Phase 2: Reduction Glucose and other organic compounds

39. LE 10-18_3 [CH 2 O] (sugar) O2O2 NADPH ATP ADP NADP + CO 2 H2OH2O LIGHT REACTIONS CALVIN CYCLE Light Input CO 2 (Entering one at a time) Rubisco 3PP Short-lived intermediate Phase 1: Carbon fixation 6 P 3-Phosphoglycerate 6 ATP 6 ADP CALVIN CYCLE 3 PP Ribulose bisphosphate (RuBP) 3 6 NADP + 6 6 NADPH P i 6P 1,3-Bisphosphoglycerate P 6 P Glyceraldehyde-3-phosphate (G3P) P1 G3P (a sugar) Output Phase 2: Reduction Glucose and other organic compounds 3 3 ADP ATP Phase 3: Regeneration of the CO 2 acceptor (RuBP) P 5 G3P

40. I had no idea I could do these things!

41. Alternative mechanisms of carbon fixation in hot, dry climates How to avoid dehydration during day? close stomata conserves water but also blocks CO 2 uptake Consequences? Positive & Negative Overall: reduces rate of photosynthesis

42. LE 10-20 Bundle- sheath cell Mesophyll cell Organic acid C4C4 CO 2 CALVIN CYCLE SugarcanePineapple Organic acids release CO 2 to Calvin cycle CO 2 incorporated into four-carbon organic acids (carbon fixation) Organic acid CAM CO 2 CALVIN CYCLE Sugar Spatial separation of stepsTemporal separation of steps Sugar Day Night CAM: Crassulacean acid metabolism

43. CAM Plants CAM plants open stomata at night, incorporating CO 2 into organic acids Stomata closed during the day CO 2 released from organic acids and used in the Calvin cycle Photosynthesis can occur during day!

44. The Importance of Photosynthesis: A Review sunlight stored as chemical energy in organic compounds by chloroplasts Sugar supplies chemical energy and carbon skeletons to synthesize other organic molecules Production of food and atmospheric oxygen

45. LE 10-21 Light CO 2 H2OH2O Light reactionsCalvin cycle NADP + RuBP G3P ATP Photosystem II Electron transport chain Photosystem I O2O2 Chloroplast NADPH ADP +P i 3-Phosphoglycerate Starch (storage) Amino acids Fatty acids Sucrose (export)