Lecture 5 - Motor Mechanism

Sliding mechanism molecular view troponin is a

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Unformatted text preview: a sarcomere •  Z lines determine the boundaries of a sarcomere –  Thick filaments made of myosin •  Myosin filaments are held in the center by 44n –  Thin filaments made of ac4n and other proteins (e.g. tropomyosin) 24 Muscle Structure  ­ Myofibrils •  Z line: regularly repe44ve structure along the myofibril that ajaches the thin filaments –  Ti4n binds to both the Z line and the thick filaments (myosin) •  A band: Region containing thick filaments (myosin) •  I band: contains por4ons of thin filaments that do not overlap thick filaments 25 Muscle Structure  ­ Myofibrils •  H zone: narrow region in center of A band, space between the 2 sets of thin filaments •  M line: in center of H zone, proteins that link central regions of adjacent thick filaments 26 Muscle  ­ Sliding mechanism •  Myofibrils increase the region where myosin and ac4n overlaps •  Ac4n filaments moves (slides) with respect to myosin filaments within a sarcomere •  Muscle with shorter sarcomere produce quicker movements but have lower shortening capacity 27 Muscle – Sliding mechanism 28 Muscle  ­ Sliding mechanism – molecular view •  Ac4n filaments –  Each ac4n protein contains a binding site for myosin –  Tropomyosin runs in the grooves formed by the ac4n helices 29 Muscle  ­ Sliding mechanism – molecular view •  Troponin is a Ca2+ ­binding protein that binds to tropomyosin and ac4n •  In the absence of Ca2+, tropomyosin will cover myosin ­binding site •  Change in conforma4on upon Ca2+ binding changes the interac4ons between tropomyosin and the ac4n filaments 30 Muscle  ­ Sliding mechanism – molecular view •  Troponin binds Ca2+ and drags tropomyosin off of myosin ­binding site and contrac4on begins •  Removal of Ca2+ reverses the process and contrac4on stops 31 Muscle  ­ Sliding mechanism  ­ Myosin •  Myosin –  Tail is interac4ng along the axis of thick filame...
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This document was uploaded on 03/05/2014.

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