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Lecture 6

Lecture 6.docx

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Western University
Biology 1002B
Tom Haffie

Lecture 6: Energy Transformation I  50% of photosynthesis on earth takes place in the water  Temperature doesn’t control phytoplankton levels in aquatic environment  Photosynthesis is… o The light dependent reduction of CO2  To sugar, carbohydrates o There are a lot of energy in sugar because there are a lot of C-H bonds, there is no energy in CO2 (fully oxidized) o This is a endergonic process, an anabolic pathway  6CO2 + 6H20 -> C6H12O6 + 6O2 o Need to know redox reactions o 6CO2 ->(reduction) -> C6H12O6 o 6H20 ->(oxidation) -> 6O2  The two phases – spatial relationship o NADPH is the reductant o Know the structure of the chloroplast o Stroma: the aqueous environment inside the chloroplast o Thylakoid membrane: where photochemistry occurs on this membrane o Thylakoid are the stacked “coins” within the chloroplast o Thylakoid lumen: inside of thylakoid o There is nothing…  Uniquely to eukaryotic, prokaryotes also does photosynthesis  Photosynthetic electron transport o Cytochrome complex between PS2 and PS1 o Many proteins are working together to make a functional photosystem o PS2: P680, PS1: P700 o When the light hits the photosystem, there is an electron acceptor at the top that grabs the excited electron  Membrane need to moist, for easier transfer of electrons o The electrons from PS2 gets transported to PS1 through an electron transport chain o And to reduce NADPH to NADP+, takes two electrons to reduce it o Oxygen evolving complex, oxygen comes from water and reduces the electron o The energy goes to pump protons o When PQ (transporter) picks up an electron from PS2 (negative) and picks up a proton from water (H), so there is no charge and can go through the membrane o Lumen have more protons than the stroma, thus create an electrochemical gradient, with the gradient, the cell is allowed to do work and we call it chemiosmosis o There is a protein called ATP synthesis that protons from Lumen can get into the stroma because of the electrochemical gradient o NADPH and ATP drives the Calvin cycle  Why do the electrons move? o They move down the chain because how they are organized based on redox potential o If redox potential is positive that means it is very strong oxidizing molecule
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