Module 4 Lecture 4 Flashcards
The ATP binding site releases the energy within an ATP. This makes myosin an?
An enzyme because it breaks down the ATP hence why the site is called myosinATPase
How does the cross-bridge cycling start?
- Low calcium concentrations when the muscle fibre is at rest
- High calcium concentration when muscle fibre is contracting
Does the ATP actually power the power stroke?
No; in fact the ATP was used before contraction even occurred to stretch the myosin head
Relaxed = myosin head is stretched
When a muscle is relaxed what is the myosin head doing?
It is fully stretched waiting for actin to become available to bind to
Analogy for the myosin head being stretched?
Stretching out an elastic band and holding it in place
What does the myosin in the power stroke section do if the elastic band analogy was still being used?
The power stroke would be the release of the elastic band so that the myosin head turns the other way
When ATP is hydrolyzed what does this mean for the myosin head?
Since the myosin head becomes stretched when ATP is attached; once the ATP is hydrolyzed that’s when the myosin head moves in the other direction which is the power stroke
What two things are required for the myosin to stretch and do the power stroke?
ATP to stretch, calcium to bind and do the power stroke
What is happening in the energized state?
Myosin head is already stretched because of the release of energy from ATP and myosin is ready to bind as long as calcium shows up
What would happen if the calcium is not released?
Myosin head that is in energized state stays in that state but does not bind to actin
What is happening to the myosin in this step?
Although the ATP was hydrolyzed which allowed the myosin head to stretch calcium also binds to the troponin to expose the actin binding site which allows myosin to stick to actin
How does myosin bind to actin once tropomyosin moves away?
Binding sites attract bindings sites; the amino acids of myosin attract the amino acids of actin
- If the myosin head is not stretched and lined up with the actin then the amino acids won’t attract
- In the elasticity analogy the myosin head that was being held in a stretched position by two pins (ADP & Pi) are now taken off which allows the myosin head to shoot back to its original position
Like two weak magnets
Why is the power stroke a “passive” process?
Not using ATP to release the myosin head, it’s just the release of energy that allows the myosin to change directions
Why does ATP serve as a key and lock?
Because it binds to myosin like a key to a lock and that unbinds the myosin head from actin
Other role of ATP: hydrolysis to transfer energy to myosin head to stretch it
If ATP is required to detach myosin from actin and then proceed to transfer energy to myosin, what would happen if ATP was not there?
Rigor mortis; the body becomes stiff
- You need ATP to relax the muscle, so if there is none your body stays in a contracted state and you die very stiff
Without ATP, SERCA does not take calcium
What is the latent period in an action potential?
When the action potential occurs but no force is generated
What happens in the contraction time?
Myosin energized, power stroke
What happens in the relaxation time?
Detachment of myosin, re-energizing, SERCA pump
