U3 Lecture 20 Flashcards
- Describe the contraction cycle (also called the cross bridge cycle) including the role of calcium and ATP in the process - Describe rigor mortis and the importance of ATP in cross bridge detachment
1
Q
Define crossbridge cycle
A
When myosin heads pull on actin towards M line
2
Q
How does the crossbridge cycle start
A
On actin - Ca2+ attaches to troponin and causes the tropomyosin to move away from the myosin binding cites on actin
On myosin - ATP binds to myosin head, ATP is hydrolyzed, and the released energy cocks the head up
3
Q
Where does crossbridge cycle take place?
A
Zone of overlap
4
Q
Contraction cycle steps
A
- Starting point : Myosin binding sites on actin become exposed when Ca2+ binds to troponin
1. Myosin heads bind to actin -> crossbridge
2. Myosin heads pivot toward center of sarcomere (power stroke)
3. ATP binds to the myosin head -> detachment of myosin head from actin (crossbridges break)
4. ATP hydrolyzed and the energy released is used to re-energize the myosin head back to its start position (cocked) for next round
Ending Point - cycle repeats until myosin binding sites on actin are no longer available
5
Q
What happens if skeletal muscle fibers run out of ATP?
A
Rigor complex and “Rigor Mortis”
6
Q
Define rigor mortis
A
when there’s not enough ATP to break the crossbridge
- muscles get stiff
