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10/10/2012 Life’s Energy Needs • All life needs a constant input of energy – Heterotrophs (Animals) • get their energy from “eating others” – eat food = other organisms = organic molecules • make energy through respiration – Autotrophs (Plants) • • • • produce their own energy (from “self”) convert energy of sunlight build organic molecules (CHO) from CO2 make energy & synthesize sugars through photosynthesis Energy Connections • Heterotrophs – Making energy and organic molecules from ingesting organic molecules glucose + oxygen carbon + water + energy dioxide C6H12O6 + 6O2 6CO2 + 6H2O + ATP OXIDATION = EXERGONIC • Autotrophs – Making energy and organic molecules from light energy carbon + water + energy glucose + oxygen dioxide 6CO2 + 6H2O + ATP C6H12O6 + 6O2 REDUCTION = ENDERGONIC Plant Needs • Need to… – collect light energy ATP • transform it into chemical energy – store light energy glucose • in a stable form to be moved around the plant or stored – need to get building block atoms from the environment CO2 • C, H, O, N, P, K, S, Mg – produce all organic molecules needed for growth H2 O N K P … • carbohydrates, proteins, lipids, nucleic acids Plant Structure • Obtaining raw materials – sunlight • leaves = solar collectors – CO2 • stomates = gas exchange – H2O • uptake from roots stomata – nutrients • N, P, K, S, Mg, Fe… • uptake from roots transpiration gas exchange 1 10/10/2012 Chloroplasts cross section of leaf leaves Plant Structure • Chloroplasts absorb sunlight & CO2 CO2 • fluid-filled interior outer membrane inner membrane stroma • Thylakoid membrane contains chloroplasts contain chlorophyll make energy & sugar Light Reactions • Light reactions • Electron Transport Chain – light-dependent reactions – energy conversion reactions • convert solar energy to chemical energy • ATP & NADPH • Calvin cycle – light-independent reactions – sugar building reactions • uses chemical energy (ATP & NADPH) to reduce CO2 & synthesize C6H12O6 ETC of Respiration • Mitochondria transfer chemical energy from food molecules into chemical energy of ATP use electron carrier NADH thylakoid granum • H+ gradient built up within thylakoid sac Photosynthesis + – double membrane – stroma – chlorophyll molecules – electron transport chain – ATP synthase chloroplast + H +H + H+ H+ H + H+ H+ HH+ H+ Hthylakoid ATP – thylakoid sacs – grana stacks chloroplasts in plant cell chloroplast thylakoid chloroplast ATP + H+ H+ H+ H+ H+ H + + + + H+ H H H H + H+ H+ H+ H+ H+ H + H+ H+ H+ + H H • There is also one on Cellular Respiration – proteins in organelle membrane – electron acceptors • NADPH – proton (H+) gradient across inner membrane • find the double membrane! – ATP synthase enzyme ETC of Photosynthesis • Chloroplasts transform light energy into chemical energy of ATP use electron carrier NADPH generates O2 2 10/10/2012 ATP Synthase • Enzyme that • moves the electrons • runs the pump • pumps the protons PHOTOSYNTHESIS (sunlight) CELLULAR RESPIRATION (breakdown of C6H12O6) • builds the gradient H+ H+ • drives the flow of protons H+ H+ H+ H+ H+ H+ through ATP synthase • bonds Pi to ADP • generates the ATP ADP + Pi ATP H+ Electromagnetic Spectrum Photosynthesis Pigments Light • Photosynthesis gets energy by absorbing wavelengths of light – chlorophyll a • absorbs best in red & blue wavelengths & least in green – accessory pigments with different structures absorb light of different wavelengths • chlorophyll b, carotenoids, xanthophylls • Chlorophylls & other pigments – embedded in thylakoid membrane – arranged in a “photosystem” • collection of molecules – structure-function relationship 3 10/10/2012 Photosystems of Photosynthesis ETC of Photosynthesis chlorophyll a • 2 photosystems in thylakoid membrane Photosystem II chlorophyll b – collections of chlorophyll molecules – act as light-gathering molecules – Photosystem II • chlorophyll a • P680 = absorbs 680nm wavelength red light Photosystem I reaction center – Photosystem I • chlorophyll b • P700 = absorbs 700nm wavelength red light antenna pigments ETC of Photosynthesis ETC of Photosynthesis thylakoid chloroplast ATP O2 sun + H+ H+ H+ H+ H+ H + + + + H+ H H H H + H+ H+ H+ H+ H+ H + + + + H+ H H H H Plants SPLIT water! 1 e e O O H e e +H e- H 2 e e O H H 1 e- H+ fill the e– vacancy Photosystem II P680 chlorophyll a Photosystem II P680 chlorophyll a ETC of Photosynthesis ETC of Photosynthesis thylakoid chloroplast + H+ H+ H+ H+ H+ H + + + + H+ H H H H + H+ H+ H+ H+ H+ H + + + + H+ H H H H ATP 3 2 e e 1 e e H+ sun 5 4 ATP H+ H+ H+ Photosystem II P680 chlorophyll a H+ to Calvin Cycle e H+ H+ + H+ H H+ energy to build carbohydrates Photosystem II P680 chlorophyll a ADP + Pi ATP e Photosystem I P700 chlorophyll b H+ 4 10/10/2012 ETC of Photosynthesis ETC of Photosynthesis electron carrier 6 e e sun sun + 5 O sun + H + H+ H H+ H+ H + H H+ H+ H+ H+ to Calvin Cycle split H2O Photosystem II P680 chlorophyll a Photosystem I P700 chlorophyll b ATP $$ in the bank… reducing power! ETC of Photosynthesis Phosophorylation • ETC uses light energy to produce – ATP & NADPH • go to Calvin cycle • PS II absorbs light – excited electron passes from chlorophyll to “primary electron acceptor” – need to replace electron in chlorophyll – enzyme extracts electrons from H2O & supplies them to chlorophyll • splits H2O • O combines with another O to form O2 • O2 released to atmosphere • and we breathe easier! Phosophorylation cyclic photophosphorylation NADP NON cyclic photophosphorylation ATP Non-cyclic Phosphorylation • Light reactions elevate electrons in 2 steps (PS II & PS I) – PS II generates energy as ATP – PS I generates reducing power as NADPH ATP ATP 5 10/10/2012 Cyclic Phosphorylation Photosynthesis (ETC) Summary • If PS I can’t pass electron to NADP…it cycles back to PS II & makes more ATP, but no NADPH 6CO2 + 6H2O + light energy C6H12O6 + 6O2 – coordinates light reactions to Calvin cycle – Calvin cycle uses more ATP than NADPH ATP 18 ATP + 12 NADPH 1 C6H12O6 There’s more to Photosynthesis than the ETC… IT’s CALVIN CYCLE TIME!!! Light Reactions • Convert solar energy to chemical energy – ATP – NADPH ATP • • • • • • • • • • Where did the energy come from? Where did the electrons come from? Where did the H2O come from? Where did the O2 come from? Where did the O2 go? Where did the H+ come from? Where did the ATP come from? What will the ATP be used for? Where did the NADPH come from? What will the NADPH be used for? Remember what it means to be a plant… • Need to produce all organic molecules necessary for growth – carbohydrates, lipids, proteins, nucleic acids • Need to store chemical energy (ATP) produced from light reactions – in a more stable form – that can be moved around plant – saved for a rainy day photosynthesis • Want to make C6H12O6 – synthesis – How? From what? What raw materials are available? • What can we do now? CO2 NADPH carbon fixation reduces CO2 NADP C6H12O6 NADP 6 10/10/2012 From Light reactions to Calvin cycle From CO2 C6H12O6 • CO2 has very little chemical energy • Calvin cycle – fully oxidized – chloroplast stroma • C6H12O6 contains a lot of chemical energy • Need products of light reactions to drive synthesis reactions stroma – highly reduced • Synthesis = endergonic process – put in a lot of energy – ATP – NADPH • Reduction of CO2 C6H12O6 proceeds in many small uphill steps ATP – each catalyzed by a specific enzyme – using energy stored in ATP & NADPH thylakoid Calvin cycle C C 1C C C C C C 3. Regeneration of RuBP C C C C C C C C C C RuBP ribulose bisphosphate starch, sucrose, cellulose & more C= C= C H H H | | | C– C– C C C C C C C C C C C C C C C C C C C RuBisCo ribulose bisphosphate carboxylase 3 ADP used to make glucose CO2 1. Carbon fixation C C C C C C 6C C C C C C C 5C glyceraldehyde-3-P G3P glucose C-C-C-C-C-C (will come in to play with Cellular Respiration) 2 2 C C C C C C 5C 3 ATP G3P C C C C PGA phosphoglycerate C C C C C C 3C 3C 6 NADP glycolysis P-C-C-C-C-C-C-P DHAP C C C C C C 3C P-C-C-C 6 ADP H | H | H | To G3P and beyond!! • Glyceraldehyde-3-P – end product of Calvin cycle – energy rich 3 carbon sugar – “C3 photosynthesis” • G3P is an important intermediate • G3P glucose carbohydrates ADP fructose-1,6bP G3P glyceraldehyde 3-phosphate C-C-C-P 6 ATP 2. Reduction 6 NADPH C C C C C C ATP Photosynthesis pyruvate 2 2 NAD+ 4 ADP 4 ATP C-C-C RuBisCo • Enzyme which fixes carbon from air – ribulose bisphosphate carboxylase – the most important enzyme in the world • it makes life out of air – definitely the most abundant enzyme lipids phospholipids, fats, waxes amino acids proteins nucleic acids DNA, RNA 7 10/10/2012 Calvin Cycle Accounting Photosynthesis summary • Light reactions • The accounting is complicated – 3 turns of Calvin cycle = 1 G3P – 3 CO2 1 G3P (3C) – 6 turns of Calvin cycle = 1 C6H12O6 (6C) – 6 CO2 1 C6H12O6 (6C) – produced ATP – produced NADPH – consumed H2O – produced O2 as byproduct • Calvin cycle – 18 ATP + 12 NADPH 1 C6H12O6 – any ATP left over from light reactions will be used elsewhere by the cell Light Reactions – consumed CO2 – produced G3P (sugar) – regenerated ADP – regenerated NADP H2O CO2 + ATP + NADPH C6H12O6 + ADP + NADP produces ATP produces NADPH releases O2 as a waste product Energy Building Reactions builds sugars uses ATP & NADPH recycles ADP & NADP CO2 ADP NADP Sugar Building Reactions NADPH NADPH ATP ATP back to make more ATP & NADPH sugars O2 Putting it all together CO2 NADP Calvin Cycle H2O + light ATP + NADPH + O2 energy sunlight ADP light + H2O + energy C6H12O6 + O2 H2O CO2 sunlight ADP Energy Building Reactions NADP Sugar Building Reactions NADPH Plants make both: energy ATP & NADPH sugars Energy Cycle sun Photosynthesis light CO2 + H2O + energy C6H12O6 + O2 PLANTS CO2 glucose H2 O ANIMAL AND PLANTS C6H12O6 O2 ATP + O2 energy + CO2 + H2O Cellular Respiration ATP ATP O2 sugars 8 10/10/2012 Photosynthesis (CC) Summary Photorespiration 6CO2 + 6H2O + light energy C6H12O6 + 6O2 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…not listed in this equation? • In most plants (C3 plants), initial fixation of CO2, via rubisco, forms a three-carbon compound • In photorespiration, rubisco adds O2 instead of CO2 in the Calvin cycle • • • • • • • • • • – Photorespiration consumes O2 and organic fuel and releases CO2 without producing ATP or sugar – Photorespiration may be an evolutionary relic because rubisco first evolved at a time when the atmosphere had far less O2 and more CO2 – Photorespiration limits damaging products of light reactions that build up in the absence of the Calvin cycle – In many plants, photorespiration is a problem because on a hot, dry day it can drain as much as 50% of the carbon fixed by the Calvin cycle C4 Plants • C4 plants minimize the cost of photorespiration by incorporating CO2 into four-carbon compounds in mesophyll cells • This step requires the enzyme PEP carboxylase • PEP carboxylase has a higher affinity for CO2 than rubisco does; it can fix CO2 even when CO2 concentrations are low • These four-carbon compounds are exported to bundlesheath cells, where they release CO2 that is then used in the Calvin cycle CAM Plants • Some plants, including succulents (cacti), use crassulacean acid metabolism (CAM) to fix carbon • CAM plants open their stomata at night, incorporating CO2 into organic acids • Stomata close during the day, and CO2 is released from organic acids and used in the Calvin cycle 9 10/10/2012 Factors Affecting Photosynthesis • • • • • Light Quality Light Intensity Light Period CO2 Availability H2O Availability The importance of Photosynthesis • The energy entering chloroplasts as sunlight gets stored as chemical energy in organic compounds • Sugar made in the chloroplasts supplies chemical energy and carbon skeletons to synthesize the organic molecules of cells • Plants store excess sugar as starch in structures such as roots, tubers, seeds, and fruits • In addition to food production, photosynthesis produces the O2 in our atmosphere Supporting a biosphere • On global scale, photosynthesis is the most important process for the continuation of life on Earth – each year photosynthesis… • captures 121 billion tons of CO2 • synthesizes 160 billion tons of carbohydrate – heterotrophs are dependent on plants as food source for fuel & raw materials 10