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

6. 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

7. 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

8. 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

9. 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

10. Photorespiration • Why? When the stomates are closed during hot-dry weather, the plant cannot get CO2 and Ribisco fixes O2 with RuBP.

11. 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

12. 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

13. C4 Plants • Ex: grass and corn • They have mesophyll cells (like C3 plants) but their chloroplasts are in Bundle-sheath cells. • Keep stomata closed most of the time b/c of hot weather to prevent water loss • Pep carboxylase fixes CO2 to produce a 4 carbon molecule in mesophyll cells

14. C4 plants • 4-carbon compound moves to the Bundle-sheath cells to make sugar. • These plants only have PSI.

16. CAM (Crassulacean acid metabolism) • Ex: cacti and pineapples • Close stomates during the day, open them at night. • Take in CO2 during the night, but do not have ATP and NADPH. So incorporate the CO2 into a variety of organic acids. • During the day, CO2 is released from the acids to be used to make sugars.

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