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Photosynthesis: Life from Light Energy needs of life All life needs a constant input of energyHeterotrophsget their energy from “eating others”consumers of other organismsconsume organic moleculesAutotrophs get their energy from “self”get their energy from sunlightuse light energy to synthesize organic molecules 2005-2006 How are they connected? glucose + oxygen  carbon + water + energy dioxide C6H12O6 6O2 6CO2 6H2O ATP  + + + Heterotrophs + water + energy  glucose + oxygen carbon dioxide 6CO2 6H2O C6H12O6 6O2 light energy  + + + Autotrophs making energy & organic molecules from light energy making energy & organic molecules from ingesting organic molecules Energy cycle Photosynthesis Cellular Respiration glucose O2 H2O CO2 ATP sun The Great Circleof Life!Where’s Mufasa? What does it mean to be a plant Need to…collect light energytransform it into chemical energystore light energyin 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,Sproduce all organic molecules needed for growthcarbohydrates, proteins, lipids, nucleic acids 2005-2006 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 Chloroplasts double membrane stroma thylakoid sacs grana stacks Chlorophyll & ETC in thylakoid membrane H+ gradient built up within thylakoid sac Plant structure H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ 2005-2006 Pigments of photosynthesis chlorophyll & accessory pigments“photosystem”embedded in thylakoid membranestructure  function Why does this structure make sense? Light: absorption spectra Photosynthesis performs work only with absorbed wavelengths of lightchlorophyll a — the dominant pigment — absorbs best in red & blue wavelengths & least in greenother pigments with different structures have different absorption spectra Photosystems Photosystems collections of chlorophyll molecules2 photosystems in thylakoid membraneact as light-gathering “antenna complex”Photosystem IIchlorophyll aP680 = absorbs 680nm wavelength red light Photosystem Ichlorophyll bP700 = absorbs 700nm wavelength red light Transfer of Electrons in PSII & PSI In PSII, the energy from the excited e- pumps H+ into the thylakoid as it moves through the ETC. Electrons from PSII are transferred to PSI. After electrons have moved through PSI, an intermediary molecule (embedded in the membrane and adjacent to PSI) transfers the e- to NADP+. A H+ is attracted to this molecule and NADPH is formed. 2005-2006 2005-2006 Chemiosmosis in Photosynthesis**(similar in Cell Respiration) proton (H+) gradient across inner membrane drive ATP formation ATP synthase enzyme Summary of the LDR PS II absorbs lightexcited electron passes from chlorophyll to “primary electron acceptor” at the REACTION CENTER.splits H2O (Photolysis!!)O2 released to atmospherePS I absorbs light Produces NADPH (stored energy) which will be used by the Calvin cycleChemiosmosis produces ATP from light energyATP will be used by the Calvin Cycle 2005-2006 ETC of Photosynthesis Chloroplasts transform light energy into chemical energy of ATP use electron carrier NADPH split H2O 2005-2006 2 Photosystems Light reactions elevate electrons in 2 steps (PS II & PS I) PS II helps generate energy as ATP (H+ pumps) PS I generates reducing power as NADPH This shows Noncyclic photophosphorylation. ETC of Photosynthesis ETC of Photosynthesis 2005-2006 Cyclic photophosphorylation If PS I can’t pass electron to NADP, it cycles back to PS II & makes more ATP, but no NADPHcoordinates light reactions to Calvin cycleCalvin cycle uses more ATP than NADPH Do Now: Light Reactions Summary Questions 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? Photosynthesis overview Light reactions convert solar energy to chemical energy ATP Calvin cycle uses chemical energy (NADPH & ATP) to reduce CO2 to build C6H12O6 (sugars) 2005-2006 From Light reactions to Calvin cycle Calvin cycle Chloroplast stroma Need products of light reactions to drive synthesis reactions ATP NADPH From CO2  C6H12O6 CO2 has very little chemical energyfully oxidizedC6H12O6 contains a lot of chemical energyreducedendergonicReduction of CO2  C6H12O6 proceeds in many small uphill stepseach catalyzed by specific enzymeusing energy stored in ATP & NADPH PGAL to make glucose 6C unstable intermediate 1C CO2 Calvin cycle 5C RuBP 3C 2x PGA/GP 6 ADP 6 ATP 3C 2x 3C x2 PGAL/G3P 6 NADP 6 NADPH 3 ADP 3 ATP Rubisco 1. Carbon fixation 2. Reduction 3. Regeneration ribulose bisphosphate ribulose bisphosphatecarboxylase sucrose cellulose etc. Rubisco Enzyme which fixes carbon from atmosphere ribulose bisphosphate carboxylase the most important enzyme in the world! it makes life out of air! definitely the most abundant enzyme Calvin cycle PGAL/G3P end product of Calvin cycleenergy rich sugar3 carbon compound“C3 photosynthesis”PGAL/G3P  important intermediatePGAL glucose   carbohydrates lipids amino acids nucleic acids 2005-2006 Photosynthesis summary Light reactions produced ATP produced NADPH consumed H2O produced O2 as byproduct Calvin cycle consumed CO2 produced PGAL/G3P regenerated ADP regenerated NADP 2005-2006 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 C6H12O6 be used for?Where did the O2 come from?Where will the O2 go?What else is involved that is not listed in this equation? 6CO2 6H2O C6H12O6 6O2 light energy  + + +