[Campbell Biology P.1178] Based on Figure 50.31, which of the following sequences accurately ... | Practice Question

Based on Figure 50.31, which of the following sequences accurately describes events in skeletal muscle contraction after the action potential triggers Ca2+ release from the SR?

  • A: Ca2+ binds to troponin; tropomyosin blocks binding sites; myosin cross-bridge forms; Ca2+ is removed from cytosol.
  • B: Ca2+ binds to troponin; myosin cross-bridge formation and breakdown occurs; Ca2+ is removed from cytosol; tropomyosin again blocks myosin-binding sites.
  • C: Myosin cross-bridge forms; Ca2+ binds to troponin; Ca2+ is removed from cytosol; tropomyosin blocks binding sites.
  • D: Ca2+ is removed from cytosol; Ca2+ binds to troponin; myosin cross-bridge forms; tropomyosin blocks binding sites.

Explanation

Following Ca2+ release Step 3 , Ca2+ binds to troponin Step 4 , which then causes myosin-binding sites to be exposed, allowing myosin cross-bridge formation and breakdown Step 5 . Subsequently, Ca2+ is removed from the cytosol Step 6 , leading to tropomyosin again blocking myosin-binding sites and muscle relaxation Step 7 .