Actin
What is the primary protein composing thin filaments in muscle contraction?
Actin
What is the primary protein composing thick filaments in muscle contraction?
Myosin
What triggers the release of calcium ions from the sarcoplasmic reticulum?
Action Potential triggers the opening of the voltage gated channels
What initiates the power stroke in muscle contraction?
Myosin
How does actin contribute to muscle force production?
Its interaction with myosin slides toward the M line
How does myosin generate force during muscle contraction?
Power stroke pull actin toward M line
How does calcium bind to troponin and initiate muscle contraction?
calcium bind to troponin C, which pulls on tropomyosin and uncover actin binding sites
How does the power stroke contribute to muscle shortening?
Pulls actin toward M line (shorten the sarcomere length)
What is the role of troponin in muscle contraction?
It covers the binding sites for myosin-actin interactions
What is the position of the myosin head configuration during muscle relaxation?
Pre-cocked/unbound
How does calcium reuptake by the sarcoplasmic reticulum lead to muscle relaxation?
Lower intracellular [calcium] allows troponin C to come back to its original conformation hiding the actin binding site
What is rigor mortis?
Without ATP, myosin remains tightly bound to actin (strongly bond state), causing this post-mortem condition.
How does tropomyosin regulate the interaction between actin and myosin?
When Ca2+ is bound to troponin, it uncovers myosin binding sites on actin
What is the effect of ATP hydrolysis on myosin cross-bridge ?
Unbind myosin from actin (break strong bound)
What is the role of DHPR in calcium regulation?
Mechanically control the opening of Ryanodine receptor (release channel)
What is the high-energy state?
After ATP hydrolysis, myosin is in this "cocked" state, ready to bind to actin.
What is the function of nebulin in sarcomere structure?
Control the length of thin filament maintain structural integrity
How does the sliding filament theory explain the role of myosin in muscle contraction?
Interaction between myosin and actin shortens the sarcomere
How does the troponin-tropomyosin complex change in the presence of calcium?
When Ca2+ is bound to troponin C, it changes tropomyosin conformation and uncover myosin binding sites on actin
What is the role of phosphate release in the power stroke (classical theory)?
Precede the power stroke (triggers strong binding state between myosin and actin)