10-28-09_photosynthesis1A - There is nothing in the dark...

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There is nothing in the dark that isn't there when the lights are on. Rod Serling Outside of a dog, a book is a man's best friend. Inside of a dog it's too dark to read. Groucho Marx The light at the end of the tunnel is the front of an oncoming train. David Lee Roth, “Perfect Timing”
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Announcements Quiz 6 is due next Monday at noon. It covers through Monday’s lecture. A second research article summary will be due on November 9 instead of the cell simulation project listed in the syllabus. Please choose a different paper from the list in Blackboard.
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H + gradient formed across inner mito. membrane using energy from electron transport The H + gradient is then used to drive ATP synthesis by ATP synthase The electron transport chain and oxidative phosphorylation do not directly make any ATP
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Mitochondria produce much of the chemical energy in eukaryotes Consists of outer and inner membranes and intermembrane space Inner membrane distinct but continuous with cristae, on which ATP synthase molecules are concentrated Due to the electron transport chain, H+ ions are concentrated in the intermembrane space.
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The proton motive force drives ATP synthesis Translocation of H+ produces two things: a pH gradient and a voltage gradient E H+ = -60 z log10[Hin/Hout] (Nernst equation) CORRECTION: Here [Hin] is for matrix and [Hout] is intermembrane space, which will give the correct sign for p 2200 p = ∆ ψ – 60 pH is the proton motive force 2200 ψ is the magnitude of the potential difference across the membrane, which is about 180 mV, pH gradient 0.5-1 pH unit For active mitochondria, p = +220 mV "+"-charged, lipid-soluble dyes such as rhodamine that distribute themselves across membranes in proportion to electric potential
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Schematic of ATP synthase Head called F1 Membrane embedded portion called F0 Actually two connecting stalks, a central and peripheral one F1 of ATP synthases contain 5 different polypeptides ( α, β, δ, γ , ε ) with the following stoichiometry ( α 3 β 3 δ γ ε ) subunits arranged alternately in F1 head like orange segments Each F1 contains 3 catalytic sites for ATP synthesis (one on each β subunit) F0 portion of ATP synthase consists of 3 different polypeptides with stoichiometry ab2c10-14, where number of c depends on species F0 F1
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Basic hypothesis of ATP formation 7.3 kcal/mole under standard conditions is needed to form ATP, but…. When substrates & product are bound to ATP synthase, G nearly 0 & thus it can occur spontaneously, without energy input Proton motive force only alters affinity of ATP for binding site, but does not contribute to ADP+Pi → ATP itself
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There are three possible states for the catalytic site on each β subunit O (open) conformation – low affinity for nucleotides, ATP is released L (loose) conformation – ADP and Pi loosely bound T (tight) conformation – ATP or ADP and Pi tightly bound
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This note was uploaded on 02/09/2010 for the course BIOL 230 taught by Professor Bartlett,e during the Fall '08 term at Purdue University-West Lafayette.

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10-28-09_photosynthesis1A - There is nothing in the dark...

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