Photosynthesis: Life from Light

1. Photosynthesis:LifefromLight

2. Energy needs of life • All life needs a constant input of energy • Heterotrophs • get their energy from “eating others” • consumers of other organisms • consume organic molecules • Autotrophs • get their energy from “self” • get their energy from sunlight • use light energy to synthesize organic molecules

3. + water + energy  glucose + oxygen carbon dioxide glucose + oxygen  carbon + water + energy  C6H12O6 + 6O2 6CO2 + 6H2O + ATP dioxide light energy  6CO2 + 6H2O + + 6O2 C6H12O6 How are they connected? Heterotrophs making energy & organic molecules from ingesting organic molecules Autotrophs making energy & organic molecules from light energy

4. sun CO2 H2O glucose O2 The Great Circleof Life! Where’s Mufasa? ATP Energy cycle Photosynthesis Cellular Respiration

5. What does it mean to be a plant • Need to… • collect light energy • transform it into chemical energy • store light energy • in a stable form to be moved around the plant & also saved for a rainy day • need to get building block atoms from the environment • C,H,O,N,P,S • produce all organic molecules needed for growth • carbohydrates, proteins, lipids, nucleic acids

6. Plant structure • Obtaining raw materials • sunlight • leaves = solar collectors • CO2 • stomates = gas exchange regulation • Found under leaves • H2O • uptake from roots • nutrients • uptake from roots

7. H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ Plant structure • Chloroplasts • double membrane • stroma • thylakoid sacs • grana stacks • Chlorophyll & ETC in thylakoid membrane • H+ gradient built up within thylakoid sac

8. Pigments of photosynthesis • chlorophyll & accessory pigments • “photosystem” • embedded in thylakoid membrane • structure  function Why does this structure make sense?

9. Light: absorption spectra • Photosynthesis performs work only with absorbed wavelengths of light • chlorophyll a — the dominant pigment — absorbs best in red & blue wavelengths & least in green • other pigments with different structures have different absorption spectra

10. Photosynthesis overview • Light reactions • convert solar energy to chemical energy • ATP • Calvin cycle • uses chemical energy (NADPH & ATP) to reduce CO2 to buildC6H12O6 (sugars)

11. Photosystems • Photosystems • collections of chlorophyll molecules • 2 photosystems in thylakoid membrane • act as light-gathering “antenna complex” • Photosystem II • chlorophyll a • P680 = absorbs 680nm wavelength red light • Photosystem I • chlorophyll b • P700 = absorbs 700nm wavelength red light

12. Light reactions • Similar to ETC in cellular respiration • membrane-bound proteins in organelle • electron acceptors • NADPH • proton (H+) gradient across inner membrane • ATP synthase enzyme

13. ETC of Photosynthesis • ETC produces from light energy • ATP & NADPH • NADPH (stored energy)goes to Calvin cycle • PS II absorbs light • excited electron passes from chlorophyll to “primary electron acceptor” at the REACTION CENTER. • splits H2O (Photolysis!!) • O2released to atmosphere • ATP is produced for later use

14. Chloroplasts transform light energy into chemical energy of ATP • use electron carrier NADPH ETC of Photosynthesis split H2O

15. 2 Photosystems • Light reactions elevate electrons in 2 steps (PS II & PS I) • PS II generates energy as ATP • PS I generates reducing power as NADPH This shows Noncyclic photophosphorylation.

16. ETC of Photosynthesis

17. ETC of Photosynthesis

18. Cyclic photophosphorylation • If PS I can’t pass electron to NADP, it cycles back to PS II & makes more ATP, but noNADPH • coordinates light reactions to Calvin cycle • Calvin cycle uses more ATP than NADPH

19. Photosynthesis summary so far… Where did the energy come from? Where did the H2O come from? Where did the electrons come from? Where did the O2 come from? Where did the H+ come from? Where did the ATP come from? Where did the O2 go? What will the ATP be used for? What will the NADPH be used for?

20. From Light reactions to Calvin cycle • Calvin cycle • Chloroplast stroma • Need products of light reactions to drive synthesis reactions • ATP • NADPH

21. From CO2 C6H12O6 • CO2 has very little chemical energy • fully oxidized • C6H12O6contains a lot of chemical energy • reduced • endergonic • Reduction of CO2C6H12O6proceeds in many small uphill steps • each catalyzed byspecific enzyme • using energy stored in ATP & NADPH

22. 1C 3C CO2 RuBP 5C 6C unstable intermediate 3 ATP PGAL to make glucose 3 ADP 3C PGA PGAL 2x x2 3C 6 ATP 6 NADPH 2x 6 NADP 6 ADP Calvin cycle ribulose bisphosphate 1. Carbon fixation 3. Regeneration Rubisco ribulose bisphosphatecarboxylase sucrose cellulose etc. 2. Reduction

23. Rubisco • Enzyme which fixescarbon from atmosphere • ribulose bisphosphate carboxylase • the most important enzyme in the world! • it makes life out of air! • definitely the most abundant enzyme

24. Calvin cycle • PGAL • end product of Calvin cycle • energy rich sugar • 3 carbon compound • “C3 photosynthesis” • PGAL  important intermediate PGAL   glucose   carbohydrates   lipids   amino acids   nucleic acids

25. Photosynthesis summary • Light reactions • produced ATP • produced NADPH • consumed H2O • produced O2 as byproduct • Calvin cycle • consumed CO2 • produced PGAL • regenerated ADP • regenerated NADP

26. light energy  6CO2 + 6H2O + + 6O2 C6H12O6 Summary of photosynthesis • Where did the CO2 come from? • Where did the CO2 go? • Where did the H2O come from? • Where did the H2O go? • Where did the energy come from? • What’s the energy used for? • What will the C6H12O6be used for? • Where did the O2 come from? • Where will the O2 go? • What else is involved that is not listed in this equation?