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SL+D103+lecture+7 - D103: Cell Biology Dr. Shin Lin Lecture...

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D103: Cell Biology Dr. Shin Lin
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D103 Fall 2011 Lecture 6 © Lin All rights reserved Lecture 7 Cytoskeleton III: Actin-Myosin Interaction, Muscle Contraction & Cell Migration Recommended Reading: MBOC (5th edition): 1010-1047 2
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D103 Fall 2011 Lecture 6 © Lin All rights reserved Actin-Based Motor Proteins: Members of the Myosin Superfamily 3
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D103 Fall 2011 Lecture 6 © Lin All rights reserved Myosin II (Prototype in Muscle) Myosin II is a dimer composed of two heavy chains and 4 light chains The head domains of the heavy chains bind and hydrolyze ATP The energy from the ATP hydrolysis is used to walk (slide) on actin filaments 4
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D103 Fall 2011 Lecture 6 © Lin All rights reserved 5 Dissection of a Skeletal Muscle (Striated Muscle) M-line Z disc Z disc sarcomere Dark band Light band A skeletal muscle cell (muscle fiber) is composed of bundles of aligned myofibrils
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D103 Fall 2011 Lecture 6 © Lin All rights reserved 6 Myosin II forms bipolar thick filaments that are organized into parallel arrays in muscle sarcomeres A sarcomere is the unit between two z-discs Sarcomeres are the repeating, contractile units in the myofibril of skeletal muscle cells Striation seen by microscopy is due to the repeating sarcomeric structure contracted sarcomere A myosin “ thick filament”
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D103 Fall 2011 Lecture 6 © Lin All rights reserved 7 Molecular Organization of a Sarcomere The actin-binding proteins, troponin complex and tropomyosin, coat actin filaments The (+) ends of actin filaments are capped by capZ and anchored at the Z discs The myosin thick filament are held in place by accessory proteins (+) (-) (+) (-)
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D103 Fall 2011 Lecture 6 © Lin All rights reserved 8 Muscle Contraction Ca 2+ binding to troponin mediates tropomyosin movement to free myosin binding site on actin ATP is hydrolyzed by the ATPase in myosin to power filament sliding
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D103 Fall 2011 Lecture 6 © Lin All rights reserved 9 Muscle contraction required both ATP and Ca 2+ In the presence of ATP, myosin head groups “walk” towards the actin filament (+) end Ca 2+ is required to make myosin binding site on actin available ==> actin and myosin filaments glide past one another without shortening. Where does the Ca 2+ come from? (+) (+) (+) (+) Animation summarizing molecular events during muscle contraction:
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D103 Fall 2011 Lecture 6 © Lin All rights reserved A myosin molecule walks along an actin filament through a cycle of structural changes 10 http://valelab.ucsf.edu/images/movies/mov- muscmyosinmotrev6.mov 10
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iClicker: If actin and myosin can generate contractile force, then… • A. Actin-myosin interaction can fully explain non-muscle cell locomotion (i.e., excluding tubulin-dependent movements). • B. Actin-Myosin interaction can provide the
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SL+D103+lecture+7 - D103: Cell Biology Dr. Shin Lin Lecture...

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