Chapter 8 – PhotosynthesisPart 1: IntroductionI. Redox reaction A. Needs a source of electrons (H2O)1. Product of oxidation of H2O is O2B. Endergonic reaction (needs energy to proceed)1. Energy comes in the form of lightII. Chloroplast Structure: A. Thylakoid1. Sub-divides a single space (like E.R.)B. Lumen1. Space inside the membrane of the thylakoidC. Stroma1. Fluid filled space inside the inner membrane but outsidethe thylakoid membraneIII. 2 Sets of Reactions in the Chloroplast A. Light Reactions: use water & light to make ATP & NADPHB. Calvin cycle/Dark reactions: use ATP, NADPH, CO2 tomake carbohydrates1. Can occur both in the light & in darkIV. NADPH – primary electron donor of photosynthesisA. NADH + PhosphateB. Electron-rich C. In the form of a di-nucleotide with an extra phosphate group:Redox ReactionChloroplastNADPHPart 2: Calvin/Benson Cycle (“Dark Reaction”)I. Introduction A. In stromaB. Uses ATP & NADPH to reduce CO2 to make carbsII. 3 Steps of Calvin Cycle A. Carbon Fixation (Carboxylation of RuBP)1. CO2 absorbed from the air is added to RuBPa. This reaction is catalyzed by rubiscoi. Most abundant enzyme on earthB. Reduction (of 3-PGA)1. Uses NADPH & ATP2. NADPHNAD+ + H+ + e-3. NADPH transfers electrons to 3-PGAC. Regeneration (of RuBP)1. 10 Triose Phosphates are rearranged to produce 6 RuBPa. Requires energy (6 ATP)III. In total, 18 ATP & 12 NADPH are needed for every 6 CO2 incorporated(12) 3-PGA [3-Carbon Compound](10) Triose Phosphate [3-Carbon Compound](6) RuBP [5-Carbon Compound]Calvin Cycle(1) -CarboxylatioRUBISCO (enzyme)6 CO2Start (3) -Regenerationof RuBP-12 NADPH & 12 ATP(2) -Reduction-6 ATPCarbohydrate Output: 2 carbs exit as 3-Carbon compounds(2) 3-Carbon carbohydratesPart 3: Light ReactionsI. Occur in Thylakoid Membrane II. Uses an electron transport chainIII. Relies on Photosystems: complexes of proteins & pigments that convert light energy to chemical energyA. Not found in mitochondriaB. 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 one2. 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 electrona. This step also produces O2 & H+b. p680 is the only protein system that can oxidize H2O5. Diagram Light particle-“antenna”--stroma--thylakoid membrane--lumen--Mn+2 complex-=pigment molecules=p680=primary electron acceptor H2O 2H + + ½O 2 + e - H+ used to create proton gradiente- donated to p680+ (after p680* is oxidized)IV. Photosystem II/Rest of Electron Transport Chain A. Electron transferred from PSII to PQB. Electron transferred to C1. Uses energy from electron to pump H+ across membraneC. C transfers electron to Pc1. Pc isn’t attached to membrane – floating around in lumenD. PS I receives what is now a low-energy electron from PcE. Light is absorbed by PS I & re-energizes electron F. Electron transferred to FDG. FD donates electron to NADP reductase to produce NADPH in stroma1. NADPH goes to Calvin cycle to be usedH. ATP synthase uses proton gradient to produce ATP in the stroma1. 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 lumenc. Formation of NADPH uses up H+ in stromaTo Calvin CycleNADP+ + H+ + 2e- NADPHADP + P ATP (NADP Reductase)(Ferredoxin)NFD-stroma-ATP SynthaseCPQ-thylakoid membrane-(Plastoquinnone)PS I (p700)-lumen-Pc(Cytochrome Complex C)(PS II)(Plastocyanin)2 H+H+= electron movement=proton (H+) movementV. Cyclic Electron Flow (^^^ is linear) A. Increases proton (H+) gradient B. Electron gets to ferredoxin (FD) normally, but then goes back to PQ1. Each time it increases the proton gradient C. Figure
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