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Lecture 19

Lecture 19: "ATP Synthesis"

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Western University
Biochemistry 2280A
Mel Usselman

Biochemistry Lecture No. 19: ATP Synthesis Tuesday October 23 , 2012 Proton Gradient & The Proton Motive Force: -Essentially, the electron transport chain pumps protons out of the mitochondrial matrix. Note that all protein complexes pump protons away from the matrix and into the intermembrane space (the concentration of protons is there). Through diffusion, the protons move from an area of high concentration to an area of low concentration (spontaneous process). This spontaneous flow of protons from the outside to the inside of the mitochondrial matrix, carrying electrical potential, is known as the proton motive force. -There are two components to the proton motive force: the concentration gradient and the electrochemical potential (where the positive charge builds up on one side of the IM membrane and the negative charge on the other). Though both components contribute to the proton motive force, it is the membrane (electrical) potential that is driving the flow of protons. The Chemiosmotic Hypothesis: -In 1961 Peter Mitchell proposed the chemiosmotic hypothesis that the proton motive force drives the synthesis of ATP. This theory explains why the destruction of the proton gradient inhibits ATP synthesis. Conversely, the creation of an artificial proton gradient stimulates ATP synthesis. F1 0ATP Synthase: -F F ATP synthase is a protein complex that allows protons to flow down their electrochemical gradient. 1 0 The energy from this proton movement is used to make ATP (made in the matrix). The rotating motion of some subunits produces ATP (transforming electrical energy to rotational energy to chemical energy). Roles Of Each ATP Synthase Subunit: -The F 0ector contains 3 subunits (ab c )2 10 functions as a proton channel, while the F sector 1 contains 5 subunits (α β ϒδε) and functions in synthesizing ATP. The rotary portion of ATP synthase is 3 3 comprised of subunits c , 10and ε, while the b subu2it helps to hold the rest of the subunits (a, α ,β , 3 3 and δ) stationary. The c s10unit is filled with lipid to provide a small enough hole for protons to flow through. ϒ is curved slightly so it does not interact symmetrically with the α andβ 3ubunit3 (This has functional implications). -In the F0sector: a helps form the proton channel (anchors b in the2membrane), b forms the 2econd stalk (the “stator”) that prevents α β3 3om rotating, and c help10form the proton channel (rotates during proton movement). -In the F1sector: α 3 3orm active sites
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