Chapter 8 Photosynthesis Part 1 Introduction I Redox reaction A Needs a source of electrons H2O 1 Product of oxidation of H2O is O2 B Endergonic reaction needs energy to proceed 1 Energy comes in the form of light II Chloroplast Structure A Thylakoid 1 Sub divides a single space like E R 1 Space inside the membrane of the thylakoid B Lumen C Stroma 1 Fluid filled space inside the inner membrane but outside the thylakoid membrane III 2 Sets of Reactions in the Chloroplast A Light Reactions use water light to make ATP NADPH B Calvin cycle Dark reactions use ATP NADPH CO2 to make carbohydrates 1 Can occur both in the light in dark IV NADPH primary electron donor of photosynthesis A NADH Phosphate B Electron rich C In the form of a di nucleotide with an extra phosphate group Redox Reaction Chloroplast NADPH Part 2 Calvin Benson Cycle Dark Reaction I Introduction A In stroma B Uses ATP NADPH to reduce CO2 to make carbs II 3 Steps of Calvin Cycle A Carbon Fixation Carboxylation of RuBP 1 CO2 absorbed from the air is added to RuBP a This reaction is catalyzed by rubisco i Most abundant enzyme on earth B Reduction of 3 PGA 1 Uses NADPH ATP 2 NADPH NAD H e 3 NADPH transfers electrons to 3 PGA C Regeneration of RuBP 1 10 Triose Phosphates are rearranged to produce 6 RuBP a Requires energy 6 ATP III In total 18 ATP 12 NADPH are needed for every 6 CO2 incorporated Calvin Cycle 1 CarboxylatioRUBISCO enzyme 6 CO2 6 RuBP 5 Carbon Compound 12 3 PGA 3 Carbon Compound Start 10 Triose Phosphate 3 Carbon Compound 2 3 Carbon carbohydrates 3 Regeneration of RuBP 12 NADPH 12 ATP 2 Reduction 6 ATP Carbohydrate Output 2 carbs exit as 3 Carbon compounds Part 3 Light Reactions I Occur in Thylakoid Membrane II Uses an electron transport chain III Relies on Photosystems complexes of proteins pigments that convert light energy to chemical energy A Not found in mitochondria B This is the part of photosynthesis that is light dependent C Light Energy Chemical Energy in 4 steps Photosystem II p680 1 Light hits pigment molecules is transferred through each one 2 Energy now in the form of a high energy electron reaches p680 turns it into p680 3 P680 transfers high energy electron to primary electron acceptor i e p680 is oxidized to p680 4 Oxidation of H2O via Mn 2 complex gives p680 a low energy electron a This step also produces O2 H b p680 is the only protein system that can oxidize H2O 5 Diagram antenna Light particle stroma lumen thylakoid membrane Mn 2 complex 2H H2O H used to create proton gradient O 2 e e donated to p680 after p680 is oxidized pigment molecules p680 primary electron acceptor IV Photosystem II Rest of Electron Transport Chain A Electron transferred from PSII to PQ B Electron transferred to C 1 Uses energy from electron to pump H across membrane C C transfers electron to Pc 1 Pc isn t attached to membrane floating around in lumen D PS I receives what is now a low energy electron from Pc E Light is absorbed by PS I re energizes electron F Electron transferred to FD G FD donates electron to NADP reductase to produce NADPH in stroma 1 NADPH goes to Calvin cycle to be used H ATP synthase uses proton gradient to produce ATP in the stroma 1 H concentration is higher in the lumen than in the stroma because a H2O is oxidized 2H in lumen in PS II b Cytochrome complex C pumps H into lumen c Formation of NADPH uses up H in stroma stroma thylakoid membrane lumen PQ C Plastoquinnone PS I p700 Pc Cytochrome Complex C Plastocyanin H PS II 2 H To Calvin Cycle NADP H 2e NADPH Ferredoxin NADP Reductase ADP P ATP FD N ATP Synthase electron movement proton H movement V Cyclic Electron Flow is linear A B Electron gets to ferredoxin FD normally but then goes back to PQ Increases proton H gradient 1 Each time it increases the proton gradient C Figure 8 15
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