Sandbox 171: Difference between revisions

Molecules of myosin aggregate in muscle cells to form thick filaments. <ref name="Lehninger">Nelson, D. and Cox, M.(2005). Lehninger Principles of Biochemistry. 4th ed. p.1119. </ref>  The rodlike structure of these thick filaments act as the core in the muscle contractile unit.  <ref name="Lehninger" /> The aggregation of several hundred myosin forms a bipolar structure which stacks in regular arrays.  Muscles consist of another protein called actin.  Actin forms the thin filament in muscle fibers.  Myosin and actin interact through weak bonds.  Without ATP bound, the myosin head binds tightly to actin.  <ref name="Lehninger" />  With ATP bound, myosin releases the actin subunit and interacts with another subunit further down the thin filament.  <ref name="Lehninger" />  This process continues in cycle, producing movement. Interaction of myosin and actin is regulated by two other proteins, tropomyosin and troponin.  <ref name="Lehninger" />

The cycle of myosin-actin interaction is outlined as follows: <ref name="Lehninger" />

 

1. ATP binds to myosin and a binding site opens on myosin head to disrupt the actin-myosin interaction, actin is released. ATP is hydrolyzed

 

2. a conformational change moving the protein to a "high-energy" state causes the myosin head to change orientation moving it to bind with the actin  subunit closer the a region called the Z disk than the previous actin subunit

 

3. the binding site is closed, strengthening the myosin-actin binding

 

4. a power stroke quickly follows and the myosin head undergoes an additional conformational change bringing it back to the resting state in which it began