Question

describe the cross bridge cycle. Make sure to include the action of actin, myosin, troponin, calcium, and ATP.

Answer 1

Cross bridge cycle represents the phenomenon of muscular contraction and relaxation which is consists of following steps:

1) Cross bridge formation

a. Activated head of myosin binds to actin forming a cross bridge between them.

b. Inorganic phosphate is released during this bridge formation between myosin and actin which makes the bond stronger.

2) Power stroke:

ADP is released and the actin activated myosin head pivot sliding the thin myofilament towards the middle of the sarcomere which causes sarcomere shortening and thus results in muscle contraction.

3) Cross bridge detachment:

Another ATP binds to the myosin head which weakens the bond between myosin head and actin. This results in detachment of myosin head and actin and muscle relaxation occurs.

4) Reactivation of myosin head:

ATP is hydrolysed to ADP and inorganic phosphate. As a result the energy which is released during hydrolysis reactivates the myosin head and causes the returning of myosin head to its cocked position.