photosynthesis Light reactions Dark reactions 1 Students will understand how energy is transformed from chemical or solar energy into the universal power source of cells ATP Focus Photosynthesis Light reactions split water capture energy from sunlight Dark reactions fix and reduce CO2 2 Overview of photosynthesis CO2 H2O C6H12O6 O2 H2O O2 e p Light Dependent Light reactions split water charge electrons make ATP and NADPH ATP NADPH H2S S e p using alternative electron donor in purple sulfur bacteria 3 Light independent dark reactions use ATP and NADPH fix CO2 Overview of photosynthesis CO2 H2O C6H12O6 O2 CO2 e p C6H12O6 ATP NADPH SAME reaction occurs in purple sulfur bacteria 4 Generic photosytem electron has increased potential energy oxidized reduced electron acceptor reduction electron transport chain antenna complex final electron acceptor electron excited in reaction center Photosystem Electron transport 5 Photopigments capture different wavelengths Green wavelengths not absorbed Blue and red highest rate 6 graph from http www life illinois edu govindjee paper fig5 gif Photosystem II makes ATP PQ Is both an electron carrier and the proton pump stroma PC lumen of thylakoids Terminology ATP created by ATP synthase via chemiosmosis and proton motive force 7 Photosystem II makes ATP Creates proton gradient Oxidized PC Powers ATP synthase ATP 8 Photosystem I makes NADPH electron transport chain NADPH Noncyclic electron flow Ultimate electron acceptor final electron acceptor 9 Electron energy PC links Photosystems I and II Photosystem I Inputs H2O and light Photosystem II 10 Electron energy PC links Photosystems I and II Outputs O2 ATP NADPH Z scheme noncyclic electron flow 11 How are ATP and NADPH used CO2 H2O C6H12O6 O2 CO2 e p C6H12O6 ATP NADPH 12 Calvin Cycle has 3 phases Fixation phase CO2 P P rubisco P P 3 phosphoglycerate x2 RuBP Endergonic or exergonic 13 Calvin Cycle has 3 phases Reduction phase ATP NADPH P P 3 phosphoglycerate ADP NADP G3P glyceraldehyde 3 phosphate Endergonic or exergonic 14 Calvin Cycle has 3 phases Regeneration phase ATP P P G3P P P RuBP ADP 15 Every turn of the Calvin Cycle fixes ONE carbon from CO2 For every 3 turns of the Calvin cycle Used to build P P P P P P 3 ATP P P P P P P RuBP 3 ADP 16 turns of the Calvin cycle are required to produce one USABLE G3P Recall that thousands of reactions are occurring simultaneously in the stroma of a chloroplast of the G3P produced can be used for other stuff of the G3P made must be used to keep cycle going 17 G3P is important in many metabolic pathways reconstitute ATP glycolysis res pir at Make starch Make fats ion fer me ge gluco nta n P Make glucose e os t n Pe Make nucleotides G3P nesis Make cellulose Make NAD and NADP tio h sp o ph e at pa w th ay Make vitamin B1 Make some amino acids Make ATP ADP make DNA RNA Make proteins build other organic molecules 18 Rubisco is a surprising enzyme Eight identical Large subunits Eight identical Small subunits Eight active sites reactions second So seconds to produce one molecule of glucose per enzyme Is Rubisco encoded by a gene If so how many 19 Rubisco is a surprising enzyme competes with CO2 at the active sites Photorespiration is the addition of to RuBP It takes energy ATP to undo this reaction Where is the O2 coming from 20 How have plants adapted to cut down on photorespiration to maximize carbon fixation Strategy ONE increase enzyme Make a TON of Rubisco Rubisco accounts for 50 of the protein in some leaves 21 How have plants adapted to cut down on photorespiration to maximize carbon fixation STRATEGY TWO move rubisco reactions away from light reactions CO2 temporarily attached to PEP carboxylase Moved to another cell released into Calvin cycle 22 How have plants adapted to cut down on photorespiration to maximize carbon fixation STRATEGY THREE store CO2 release it all at once to concentrate it CO2 temporarily stored as organic acid at night when stomata are open CO2 released into Calvin cycle during the day when stomata are closed 23 How have plants adapted to cut down on photorespiration to maximize carbon fixation STRATEGY FOUR shrug and deal with it then find a way to use the products in other processes like cell cell signalling and development 24 You should be able to Tell me the main input and output molecules of both light and dark reactions of photosynthesis explain why light reactions need water but not CO2 and why the dark reactions need CO2 but don t produce O2 and why organisms that use a different electron donor than water will NOT release O2 but will still need CO2 Tell me how photosynthesis works highlighting the roles of the proteins molecules of interest Photosystem I and II pigments PC PQ pheophytin ferrodoxin rubisco NADP ATP RuBP G3P Explain why the two photosystems work best when they work together and predict the effect of removing PC from the system blocking Photosystem II s electron transport chain shining light of only one wavelength on the photosystems green vs blue or red putting a proton channel in the thylakoid membrane to allow protons another way to diffuse across the membrane 25 You should be able to Tell me the differences and similarities of photosystem I and II and what links them together Tell me the ultimate electron acceptors in all ETCs for respiration and photosystems I and II Predict what would happen if any of these acceptors were missing Predict which parts of respiration and photosynthesis would be affected by poisons that affect the ETCs Which parts could continue Tell me where all these reactions occur Answer questions about the amino acid composition of proteins in these structures membrane proteins enzymes in the pathways effects of mutations Answer questions about the hydrophobicity or otherwise of any component of the light reactions and dark reactions hint light related proteins are in the membrane dark reactions are in the stroma Answer structure function relationship questions about the photosystems and the chloroplast in general 26 You should be able to Explain in general terms how the Calvin Cycle works Why most of the G3P produced at any given time is stuck in the cycle Why it takes six cycles to make one molecule of glucose How RuBP is reconstituted Where reduction occurs How plants in hot climates can decrease the amount of photorespiration through C4 pathways Answer questions about rubisco as an enzyme what might affect the rate of reaction competitive inhibition by O2 that it s encoded by genes and