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ATP synthesis

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Biochemistry 2280A
Eric Ball

15 – ATP synthesis Proton gradient from electron transport chain • Electron transport chain pumps protons out of the mitochondrial matrix • Intermembrane space pH ~ 7, Matrix pH ~ 8; intermembrane more acidic therefore more protons Proton Motive Force • Two components: • Concentration gradient ○ More protons in intermembrane space, they want to diffuse to lower concentration • Electrical potential ○ Consequence of the fact that proteins are positive and there is no counter ion being moved across the membrane with them; accumulates a positive charge on the intermembrane space side of the inner mitochondrial membrane ○ Positives want to get into the more negative side  membrane potential • Electrical potential contributes more strongly then the concentration difference.  Chemeosmotic hypothesis: protonmotive force drives the synthesis of ATP: destruction of proton gradient inhibits ATP synthesis F1F 0TP synthase • A protein complex that allows protons to flow down their electrochemical gradient • The energy from this proton movement is used to make ATP; couples movement of protons to ATP synthesis • ATP is made in the matrix • Smallest rotary motor we know E.coli F1F 0 F 0rotor • Peripheral • Transmembrane section membrane section • 3 subunits: ab c • 5 subunits: 2 10 • Proton channel α 3 γ3δ ε F 1 stator • Makes ATP ○ Each c subunit binds one proton ○ Ring of c subunits rotates in membrane, moving protons to a channel formed with α subunit, allowing protons to be released into matrix ○ γ and ε subunits (control stalk) rotate with the c subunits, and the long curved α -helicesfrom the γ subunit extended into the α β 3 3hexamer and causing a conformational change in the β subunits ○ Each β subunit has a catalyrtic site for ATP synthesis, and the conformation changes drive synthesis of ATP from ADP and Pi ○ The α 3 3hexamer is prevented from rotating by a “peripheral stalk”, composed of the two b subunits and δ ○ Long slender b subunits anchored to a subunit in membrane and δ helps bind b to α β 3 3 Roles of
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