1. Skeletal Muscle Contraction Sliding Filament Model actin myosin Fig. 11.3

2. Thin (actin) filament actin monomer G-actin (globular actin) actin polymer F-actin (filamentous actin) from Alberts et al., Molecular Biology of the Cell Fig. 11.3 Fig. 3-3 Ganong      

3. Thick (myosin) filament myosin molecule (“monomer”): 2 heavy chains + 4 light chains Fig. 11.3 from Alberts et al., Molecular Biology of the Cell central bare zone

4. Striated Muscle A- band (anisotropic) contains thick filaments (and portions of thin filaments) I- band (isotropic) contains thin filaments Fig. 3-2 Ganong Fig. 3-3 Ganong Fig. 11.1

5. Striated Muscle Fig. 11.4

6. Striated Muscle Fig. 11.2

7. Sliding Filament Model of Contraction Fig. 3.3 Ganong Fig. 11.9

8. Cross Bridge Cycle Fig. 11.9 As myosin heads bind ATP, the crossbridges detach from actin, become reoriented and hydrolyze ATP to ADP and P i. No ATP  no detachment e.g., rigor mortis The myosin head is an ATPase. The two most important shape-changing events are 13/10 ATP binding (which leads to detachment and reorientation) 11/12 P i release (which leads to the power stroke) causes P i to be released. Power stroke causes ADP to be released PiPi

9. ATP binding to myosin Fig. 3-6 Ganong (19 th edition) The image above and the modifications to the Saladin text in the previous slide are based on Raiment et al., Science 261:50-58, 1993, and Vale and Milligan, Science 288:88-95, 2000. (see also Fig. 16.58 in Alberts et al., Molecular Biology of the Cell, 4 th ed., 2002) ATP binding is more important for reorientation than ATP hydrolysis. 

10. Length-Tension Relationship Increased muscle length causes decreased overlap between thick and thin filaments. Increased muscle diameter causes increased separation (the lattice spacing) between thick and thin filaments. (actual mechanism still a topic of debate, see Fuchs and Martyn, Length- dependent Ca 2 + activation in cardiac muscle: some remaining questions. J. Muscle Res. and Cell Motility, 26:199-212, 2005) = normal operating length for skeletal muscle = normal operating length for cardiac muscle Fig. 11.11 ly short