Myosin and actin filaments


Myosin and actin filaments

Muscle contraction involves myosin and actin filaments sliding over one another - 

Myosin filaments:

  • Myosin filaments have globular heads that are hinged, so they can move back and forth. 
  • Each myosin head has a binding site for actin and a binding site for ATP

Actin filaments:

  • Actin filaments have binding sites for myosin heads, called actin-myosin binding sites.
  • Another protein called tropomyosin is found between actin filaments. It helps myofilaments move past each other. 

Binding sites in resting muscles:

For myosin and actin filaments to slide past each other, the myosin head needs to bind to the actin-myosin binding site on the actin filament. 

In a resting muscle, the actin-myosin binding site is blocked by tropomyosin. This means myofilaments can't slide past each other because the myosin heads can't bind to the actin filaments.

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