lec_19_slides

# lec_19_slides - Sliding Filament Model Myosin filament...

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Sliding Filament Model Myosin filament Myosin head Actin binding site Actin filament x k + Rate constants k - x As the actin filament moves past the (fixed) myosin filament, the myosin head can bind to it at the red triangle. When it does, the springs are either stretched or compressed and a force x acts at the binding site. Equations governing the probability n(x,t) that a cross-bridge is attached dn ( x , t ) = n ( x , t ) v n ( x , t ) = [ 1 n ( x , t ) ] k + ( x ) n ( x , t ) k ( x ) dt t x Formation of new Detachment of existing bonds bonds At steady state [ n = n(x) ] v dn ( x ) = [ 1 n ( x ) ] k + ( x ) n ( x ) k ( x ) dx k + k + = attachment rate; k - = k - detachment rate; n = probability of attachment x h 1

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x > h : In this region the actin binding site is approaching the free myosin head, unoccupied. Since both k + and k - are zero, no binding occurs: n(x) = n(h) = 0 h-x 0 < x <h : If binding is to occur, it has to do so (according to this simple model) within this narrow region where the binding rate constant is large, described by the equation: v dn = ( 1 n ) k + 0 dx k + k - 0 k + x 0 n ( h x 0 ) = 1 exp v x h 0 < x < h-x 0 Both the attachment and detachment rate constants are zero, so the myosin head can neither bind to nor detach from an actin filament, and the probability of attachment remains constant: n(x) = n(h-x 0 ) = constant x < 0 As the complex moves into the region x < 0 , the force of interaction sustained at the actin-myosin bond changes sign and its probability of attachment begins to fall, as described by the equation: v dn =− k 0 n k + k - k x k + 0 x 0 ⎞⎤ k x dx
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## This note was uploaded on 11/11/2011 for the course BIO 20.410j taught by Professor Rogerd.kamm during the Spring '03 term at MIT.

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lec_19_slides - Sliding Filament Model Myosin filament...

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