L24 - Monday,November22,2010...

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Monday, November 22, 2010 Cell Movements II: Muscle Contraction Reading: Chapter 17, pages 597 - 604  Objectives Myosins are members of a  family  of related proteins. This family includes about a  dozen  classes , including:  o type I myosins monomeric transport organelles along actin filaments o type II myosins dimeric present in muscle All myosins share a conserved head domain, which includes the actin- and ATP- binding sites. The tail domains are more divergent.  o In myosin II, the tail domains wrap around each other to form a rod-like  coiled coil .  2 or more alpha helices. Like a cytoskeletal element. Skeletal muscle is composed of muscle fibers, which are fused multinucleate cells.  o Each muscle fiber contains a number of  myofibrils . 1 cell thick. Muscle  progenitors undergo end to end fusion. Each muscle fiber contains multiple  strands called myofibrils.  o Myofibrils are composed of repeating units called  sarcomeres . repeating  units. Thus striated muscle.  o A sarcomere contains an ordered hexagonal array of  thick and thin  filaments Thick filaments o composed of a staggered, parallel array of myosin II molecules o myosin heads project out to the side to form  cross-bridges  that link up to  actin. Project outward. Enable to bind to thin filaments.  Opposite  directions. Thick filament spans the length of a sarcomere. Bare region no 
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