Ch 10 Photosynthesis--> To make with light!

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

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

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

4. Reaction: 6CO2 + 12H2O + light --> C6H12O6 + 6O2 + 6H2O glucose Simplest rxn: CO2 + H2O + light --> [CH2O] + O2 carbohydrate Photosynthesis: conversion of light energy into chemical energy Simplified rxn: 6CO2 + 6H2O + light --> C6H12O6 + 6O2

5. Enters through roots Leaf cross section Vein Mesophyll Stomata O2 CO2 Mesophyll cell Chloroplast 5 µm Outer membrane Thylakoid Intermembrane space Thylakoid space Stroma Granum Innermembrane 1 µm 6CO2 + 6H2O + light --> C6H12O6 + 6O2 Exits through stomata Organic molecule for fuel or other Gas enters through stomata LE 10-3 or used in respiration

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

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

8. in chlorophyll a CH3 in chlorophyll b CHO LE 10-10 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. Chlorophyll a LE 10-9a Chlorophyll b Carotenoids Absorption of light by chloroplast pigments 400 700 500 600 Wavelength of light (nm) Absorption spectra

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 O2 is a product?

11. LE 10-9c Aerobic bacteria Filament of algae 600 500 700 400 Engelmann’s experiment (1883): Action spectrum 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. Light-Induced Excitation: • 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

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

15. Light-dependent rxn: in thylakoid LE 10-5_1 H2O Light LIGHT REACTIONS Chloroplast

16. LE 10-5_2 H2O Light LIGHT REACTIONS ATP NADPH Chloroplast O2

17. Calvin cycle: in stroma LE 10-5_3 H2O CO2 Light NADP+ ADP + P i CALVIN CYCLE LIGHT REACTIONS ATP NADPH Chloroplast [CH2O] (sugar) O2

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 H2O Light -independent (aka dark or Calvin cycle)(in stroma): Synthesis of organic molecules from CO2 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. Thylakoid Photosystem STROMA Photon LE 10-12 Light-harvesting complexes Reaction center Primary electron acceptor e– Thylakoid membrane Special chlorophyll a molecules Pigment molecules Transfer of energy THYLAKOID SPACE (INTERIOR OF THYLAKOID)

22. H2O CO2 Light NADP+ ADP CALVIN CYCLE LE 10-13_1 LIGHT REACTIONS ATP NADPH O2 [CH2O] (sugar) Primary acceptor Once P680 is oxidized (gives up e-), is it functional? How is it restored to functionality? e– Energy of electrons Light P680 Photosystem II (PS II)

23. H2O CO2 Light NADP+ ADP CALVIN CYCLE LE 10-13_2 LIGHT REACTIONS ATP NADPH O2 [CH2O] (sugar) Primary acceptor e– H2O 2 H+ + O2 1/2 e– Splitting of H2O yields e- that fill e-”hole” in oxidized P680 e– Energy of electrons Light P680 Photosystem II (PS II)

24. H2O CO2 Light NADP+ ADP CALVIN CYCLE LE 10-13_3 LIGHT REACTIONS ATP NADPH O2 [CH2O] (sugar) Primary acceptor Electron transport chain Pq e– H2O Cytochrome complex 2 H+ + O2 1/2 Pc e– e– Energy of electrons Light P680 ATP Photosystem II (PS II)

25. H2O CO2 Light NADP+ ADP CALVIN CYCLE LE 10-13_4 LIGHT REACTIONS ATP NADPH O2 [CH2O] (sugar) Primary acceptor Primary acceptor Electron transport chain e– Pq e– H2O Cytochrome complex 2 H+ + O2 1/2 Pc e– P700 e– Energy of electrons Light P680 Light ATP Photosystem I (PS I) Photosystem II (PS II)

26. H2O CO2 Light NADP+ ADP LE 10-13_5 CALVIN CYCLE LIGHT REACTIONS ATP NADPH Electron Transport chain O2 [CH2O] (sugar) Primary acceptor Primary acceptor Electron transport chain Fd e– Pq e– e– e– NADP+ H2O Cytochrome complex 2 H+ + 2 H+ NADP+ reductase + NADPH O2 1/2 Pc e– + H+ P700 Energy of electrons e– Light P680 Light ATP Photosystem I (PS I) Photosystem II (PS II)

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

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 Primary acceptor Primary acceptor Fd Fd NADP+ Pq NADP+ reductase Cytochrome complex NADPH Pc Photosystem I ATP Photosystem II

32. How is ATP made? By chemiosmosis

33. H2O CO2 Light NADP+ ADP CALVIN CYCLE LIGHT REACTIONS LE 10-17 ATP NADPH O2 [CH2O] (sugar) STROMA (Low H+ concentration) Cytochrome complex Photosystem I Photosystem II Light NADP+ reductase Light 2 H+ NADP+ + 2H+ Fd NADPH + H+ Pq Pc H2O O2 1/2 THYLAKOID SPACE (High H+ concentration) 2 H+ +2 H+ To Calvin cycle Thylakoid membrane ATP synthase STROMA (Low H+ concentration) ADP + ATP P i H+

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? CO2

36. Calvin cycle • Three phases: • Carbon fixation (catalyzed by rubisco) • Reduction Regeneration of the CO2 acceptor (RuBP)

37. LE 10-18_1 H2O CO2 Input Light (Entering one at a time) 3 NADP+ CO2 ADP CALVIN CYCLE LIGHT REACTIONS ATP Phase 1: Carbon fixation NADPH Rubisco O2 [CH2O] (sugar) 3 P P Short-lived intermediate P 6 3 P P 3-Phosphoglycerate Ribulose bisphosphate (RuBP) 6 ATP 6 ADP CALVIN CYCLE

38. H2O CO2 Input Light (Entering one at a time) 3 NADP+ CO2 ADP CALVIN CYCLE LIGHT REACTIONS LE 10-18_2 ATP Phase 1: Carbon fixation NADPH Rubisco O2 [CH2O] (sugar) 3 P P Short-lived intermediate P 6 3 P P 3-Phosphoglycerate Ribulose bisphosphate (RuBP) 6 ATP 6 ADP CALVIN CYCLE 6 P P 1,3-Bisphosphoglycerate 6 NADPH 6 NADP+ 6 P i P 6 Glyceraldehyde-3-phosphate (G3P) Phase 2: Reduction Glucose and other organic compounds 1 P G3P (a sugar) Output

39. H2O CO2 Input Light (Entering one at a time) 3 NADP+ CO2 ADP CALVIN CYCLE LIGHT REACTIONS LE 10-18_3 ATP Phase 1: Carbon fixation NADPH Rubisco O2 [CH2O] (sugar) 3 P P Short-lived intermediate P 6 3 P P 3-Phosphoglycerate Ribulose bisphosphate (RuBP) 6 ATP 6 ADP 3 ADP CALVIN CYCLE 6 P P 3 ATP 1,3-Bisphosphoglycerate 6 NADPH Phase 3: Regeneration of the CO2 acceptor (RuBP) 6 NADP+ 6 P i P 5 G3P P 6 Glyceraldehyde-3-phosphate (G3P) Phase 2: Reduction 1 P G3P (a sugar) Glucose and other organic compounds Output

40. I had no idea Icould do these things!

41. Alternative mechanisms of carbon fixation in hot, dry climates • How to avoid dehydration during day? • close stomata Consequences? Positive & Negative • conserves water • but also blocks CO2 uptake Overall: reduces rate of photosynthesis

42. LE 10-20 CAM: Crassulacean acid metabolism Sugarcane Pineapple CAM C4 CO2 CO2 Night Mesophyll cell CO2 incorporated into four-carbon organic acids (carbon fixation) Organic acid Organic acid Bundle- sheath cell Day CO2 CO2 Organic acids release CO2 to Calvin cycle CALVIN CYCLE CALVIN CYCLE Sugar Sugar Spatial separation of steps Temporal separation of steps

43. CAM Plants • CAM plants open stomata at night, incorporating CO2 into organic acids • Stomata closed during the day • CO2 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. Light reactions Calvin cycle H2O CO2 LE 10-21 Light NADP+ ADP + P i RuBP 3-Phosphoglycerate Photosystem II Electron transport chain Photosystem I ATP G3P Starch (storage) NADPH Amino acids Fatty acids Chloroplast O2 Sucrose (export)