Exam #3: Sliding Filament Theory

Question 1

Step #1:

Answer 1

Before contraction begins, an ATP molecule binds to the myosin heads of the cross bridges

Question 2

Step #2:

Answer 2

The ATPase enzyme activity of the myosin head immediately cleaves the ATP but the ADP+P remains bound to the head, so that the myosin head is in a high energy state, ready to bind to the actin active site

Question 3

Step #3:

Answer 3

When the troponin-tropomyosin complex binds with calcium ions (from the SR) the tropomyosin is affected to “uncover” the active sites on the actin filaments allowing the attachment of the myosin heads

Question 4

Step #4

Answer 4

Myosin heads bind to active site on the actin filaments

Question 5

Step #5

Answer 5

The bond between the head of the cross bridges (myosin) and the actin filaments causes the bridge to change shape, bending the 45 degrees inwards of the sarcomere (POWER STROKE)

Question 6

Step #6

Answer 6

The power stroke pulls the thin filaments inward only a small distance

Question 7

Step #7

Answer 7

Once the head tilts, this allows release of ADP and phosphate ions

Question 8

Step #8

Answer 8

At the site of release of ADP, a new ATP binds, which causes the detachment of the myosin head from the actin active site

Question 9

Step #9

Answer 9

A new cycle of attachment-detachment-attachment begins as long as calcium ions and ATP are available

Question 10

Step #10

Answer 10

Repeated cycles of cross-bridge binding, bending, and detachment complete the shortening/tension contraction of the muscle fiber