MUSCLES AND ATP

1)

• Muscle contracts:

– Occurs because of sliding of thin filaments over and between thick filaments towards center.

- Shortening the distance from Z disc to Z disc.

• A bands:

– Contain actin.

– Move closer together but do not shorten.

• I bands:

– Distance between A bands of successive sarcomeres.

– Decrease in length.

• H bands:

– Contain only myosin.

– Shorten during contraction..

2)

• Myosin binding site splits ATP to ADP and Pi.

• ADP and Pi remain bound to myosin until myosin heads attach to actin.

• Pi is released, causing the power stroke to occur.

• Power stroke pulls actin toward the center of the A band..

3)

• ADP is released, when myosin binds to a fresh ATP at the end of the power stroke.

• Release of ADP upon binding to another ATP, causes the cross bridge bond to break.

• Cross bridges detach, ready to bind again.

• Synchronous action:

– Only 50% of the cross bridges are attached at any given time..

4)

These cross bridges formation are regulated by tropomyosin/troponin and calcium level.