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Lecture 5

2012.02.11 - Bio 1202 Lecture 5 Review Notes.docx

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Biology 1202B
Gardiner/ Murphy

Lecture 5  Noncyclic electron flow: o 1) 1 H2O splits and creates 1 ATP and 1 NADPH o 2) 1 photon to drive 1 electron through 1 photosystem o When H O2splits it creates 2 electrons o 1 electron through 2 photosystems requires 2 photons o 2 electrons through 2 photosystems requires 4 photons o To produce 1 O2would require 8 photons  Cyclic electron flow – under certain conditions photoexcited electrons from photosystem I can take this alternative pathway o Excited electrons cycle from their reaction centre to a primary acceptor, along an electron transport chain and returns to the oxidiz700chlorophyll o As electrons flow along the electron transport chain, they generate ATP by cyclic photophosphorylation  Noncyclic produces ATP and NADPH in roughly equal quantities o But, the Calvin cycle consumes more ATP than NADPH  Cyclic allows the chloroplast to generate enough surplus ATP to satisfy the higher demand of ATP in the Calvin cycle  Chemiosmosis – the mechanism by which chloroplasts and mitochondria generate ATP o Oxidative phosphorylation – mitochondria o Photophosphorylation – chloroplast  Electrons pass down the ETC +  Cytochrome complex pumps H from stroma to thylakoid lumen  H is high concentration in lumen and low concentration in stroma +  Also H comes from the splitting of water molecules  This causes an electrical gradient  Proton-motive force: provides energy for ATP synthase  Photosynthesis: carbon dioxide + water + light  glucose and oxygen  Calvin cycle: o Reactions occur in the chloroplast stroma and the enzyme is Rubisco o Light independent reaction o Rubisco attaches the carbon from CO2to ribulose bisphosphate  Rubisco is the most common and complex protein on the Earth o The Calvin cycle uses ATP and NADPH to convert CO2to sugar o The starting material is regenerated at the end of the cycle, so it can continue o The sugar product is not glucose, it is a three-carbon sugar (glyceraldehyde-3- phosphate or G3P) o Each turn of the cycle fixes one carbon o
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