Clicker questions • Clicker channel: 70 • Response Ware Session ID: psio201Which of the following elements of the sarcomere does not change in length when the muscle contracts? 1. A band 2. I band 3. H zone 4. Zone of overlap 1. 2. 3. 4.94%0%1%5%Which of the following is a contractile protein of muscle? 1. myosin 2. myomesin 3. tropomyosin 4. all of the above 1. 2. 3. 4.87%6%7%0%Myofibrils are A. elements inside the sarcomere that form cross bridges. B. made of sarcomeres arranged end to end and found inside the muscle fiber. C. bundles of muscle fibers surrounded by perimysium. A. B. C.5%92%3%Lecture 18: Cellular Basis of Muscle Contraction Office hours: Tuesday and Thursday 1-2pm in Gittings 108 or by appointment Claudia Stanescu, Ph.D.Objectives (pp. 301-304, sec 10.3): 1. Describe the contraction cycle including the role of calcium and ATP in the process. 2. Describe rigor mortis and the importance of ATP in cross bridge detachment.Crossbridge Cycling Cycle is entered following exposure of myosin binding sites on the actin thin filament (regulatory role for Ca2+) Prior to entering the contraction cycle – at the end of the last muscle contraction: 1) ATP binds to the myosin head 2) This ATP is hydrolyzed by the unbound head, and the released energy results in a conformational ‘cocking’ of the head group (the ADP and Pi remain bound to the cocked head) http://www.bms.ed.ac.uk ‘Ready to bind’Where does crossbridge cycling take place?Crossbridge CyclingThe contraction cycle begins when Ca2+ is released from the SR, binds to troponin and the myosin binding sites on actin are exposed Starting point muscle is ready to contract because myosin heads are ‘cocked’ and binding sites are exposed 4 1 2 3Contraction cycle steps: 1) Myosin binding sites on actin become exposed when Ca2+ binds to troponin 2) Myosin heads bind to actin forming crossbridges 3) Myosin heads pivot toward the center of the sarcomere (power stroke) 4) ATP binds to the myosin head detachment of myosin head from actin (crossbridges break) 5) ATP is hydrolyzed and the energy released is used to re-energize the myosin head back to its start position (‘cocked’) so a new crossbridge can form 6) The contraction cycle repeats until the myosin binding sites on actin are no longer availableMuscle contraction animation Cross-Bridge Cycle animation (captioned): http://www.youtube.com/watch?v=Tuzr5N0TInMRigor complex The attached head group after the power stroke is called a rigor complex Rigor mortis – the rigor of death because of lack of ATP to detach the crossbridge 2ATP is needed to detach the cross bridge 2 3Suggested Learning Activities • Draw the 4 step contraction cycle and describe the events at each step • Watch the muscle contraction animation with your notes in front of you. Pause the video and review each step described • Using your arm and forearm as the myosin protein, act out the cross bridge cycle with a classmate explaining the events that occur at each
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