11-07-08_photosynthesisA

11-07-08_photosynthesisA - Poetry is the synthesis of...

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Poetry is the synthesis of hyacinths and biscuits.  Carl Sandburg Among the “Top Ten reasons that Homer Simpson  should be President” – Homer on Letterman I will take full advantage of the free food that  comes with the job. I have enormous experience apologizing for failed  decisions. I will appoint a Secretary of Donuts. I will be the Secretary of Donuts.
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Announcements Quiz 5, version 2 due at 5 pm today Quiz 6 due at noon on Monday
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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+ = -59 z log10[Hin/Hout] (Nernst  equation) p =  ψ  – 59  pH is the proton  motive force ψ  is mitochondrial membrane  potential, which is about -180 mV For active mitochondria,                   p = 220 mV and pH gradient  0.5-1  pH unit So about 80%  p from voltage  gradient and 20% from pH "+"-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 )   α & β  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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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 At any given time, the catalytic sites for the three  β  subunits are each in  different conformations, such that one is in L, one is in T, and one is in O  Each site passes sequentially from L to T to O and then back to L
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Simultaneous tracking of conformational changes Movement of H+ through F0 drives conformational changes Notice that gamma subunit is rotating during this, 360 °  for one cycle 3 molecules ATP/full rotation, since each site will undergo ATP  synthesis
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How do the protons drive the rotation in F0?
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