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Lecture 21

BIOC13H3 Lecture 21: BIOC13 Lecture 21

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Biological Sciences
Jason Brown

BIOC13 Lecture 21 ATP Synthase  ATPase usually means you are breaking atp down, so the atp synthase can take atp, hydrolyze it and use it to pump protons and create a gradient  Atp synthase structure is peculiar or unusual  We have the Fo domain, embedded in the inner mitochondrial membrane  Also have the F1 domain sticking out in the matrix  Each of these domains has many different proteins  F1 is made up of 3 alpha subunits, 3 beta subunits, 1 gamma subunit, 1 delta and 1 epsilon  Fo is also made up of multiple subunits, a, b, F6 etc and C subunits  There can be different c subunits in different organisms (from 8-15)  Delta and epsilon are there to link F1 and Fo domain  Function of Fo part is to translocate protons, allows protons to flow across the membrane and there is free energy released and use that to synthesize atp  The atp synthesis is done by f1 domain (catalytic domain)  Atp synthase is a reversible reaction, so it can run the other way to break down atp and thereby contribute to forming a proton gradient  Fo stands for oligomycin, which blocks the ability of fo domain to move protons and so the action of it is blocked, no energy to drive synthesis of atp  F1 domain uses the binding change mechanism  We have alpha beta subunits  The alpha are not thought to play any role in direct atp formation, they might play a role in regulating the enzyme  It’s the 3 beta that play a role in synthesizing atp  Each beta unit alternates between 3 different conformations  In open, things are able to bind the pocket on the subunit, but they don’t stick so we have binding and also releasing  Loose conformation, where adp and pi are bound there, they are stuck there, so no longer any release  Tight configuration, you can imagine that the adp and pi are squeezed together, which causes their synthesis to occur, but then the atp is stuck there  As we go through those conformations we get atp production  The central point has an asymmetrical structure, it will spin around and as that happens it will cause the beta subunits to change conformation  Alternates from open, to loose, to tight  When hydrolysing atp we go in the opposite direction (clockwise)  For every 1 full rotation, you will get 3 atp produced  This is the same for every atp, 3 atp/ 1 gamma rotation  How does the rotation cause the beta to change conformation?  The beta are being shown in one of the different conformation  Where you see Badp, that is loose conformation, Batp is tight, bE is open (empty)  As we go to the next picture, the gamma has rotated  As the gamma rotates, the structure of the part that is shown to the beta is different in each of the 3 pictures  As it shows different faces to beta, the beta changes its response based on the face shown  The gamma then has to be asymmetrical, otherwise the mechanism wont work  This is the only enzyme that works in such a way (rotation in the middle) 
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