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What happens to the sarcomere if the ATP cannot bind to the myosin head?
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When myosin cross bridges bind to actin what happens?
Muscle contraction results
What triggers the binding of myosin to actin?
Calcium ions bind to troponin and change its shape.
What does calcium bind to in smooth muscle contraction?
Calcium binds to the messenger protein Calmodulin. The calcium-calmodulin complex then activates myosin light chain kinase (MLCK), which phosphorylates myosin to allow it to bind to actin - producing contraction.
What is atrial depolarization?
Atrial depolarization is the first part of the cardiac cycle.Cardiac (and skeletal) muscle is made up of bundled stands of functional units called sarcomeres. Each sarcomere consists of two Z-disks, which mark the ends of each sarcomere, and alternating dark and light bands called A-bands and I-bands respectively. The I-band contains only actin (the main cytoskeletal protein in most cells) filaments whereas the A-band contains overlapping myosin (a "molecular motor" protein) and actin filaments in its periphery and only myosin filaments in the central region called the H-zone. The center of the H-zone is marked by an imaginary line (called the M-line) in which myosin extends in both directions. The sarcomere contracts inward toward the M-line. "Depolarization" occurs when an electrochemical event causes calcium cations to be released from a membranous network (similar to the the endoplasmic reticulum) called the sarcoplasmic reticulum and creates an action potential. The free Ca2+ binds to a specific troponin protein shifting a troponin/tropomyosin protein complex allowing the myosin head groups to bind to the actin filament. ATP hydrolysis causes conformational changes of the myosin filament which in effect "pulls" the actin filament toward the M-line of the sarcomere. The sarcomere can return to its resting potential by allowing potassium (K+) ions to flow out.
What happens when calcium ions bind to troponin?
When Ca2+ ions are released from the sarcoplasmic reticulum, They combine with troponin, and this cause the tropomyosin threads to shift their position
What unmasks troponin protein?
Ca 2+ ions released from the sarcomeres ER bind to troponin and force a conformational change that opens the way for myosin to bind to actin.
What specific event triggers the uncovering of the myosin site on actin?
Calcium ions bind to troponin and change its shape.
What molecule has a binding site for myosin heads?
Myosin heads bind to the actin binding site, and also has a part where ATP binds
What molecule must bind to to the cross bridge in order for it to disconnect with actin?
The molecule that binds to myosin, which causes it to disconnect, is an ATP molecule
Does myosin have the ability to swivel when powered by ATP?
Yes...ATP causes myosin to detach from actin. Then, Hydrolysis of ATP, which results in ADP and P, causes conformational change in myosin head to swivel or pivot about its axis and then weakly bind to an actin filament. Once the myosin head binds, a conformational change in the myosin head will cause the P to leave (the ADP is still stuck on). The leaving of the P causes the power stroke or "the pulling of the actin filament/rowing stroke". ADP then leaves and the myosin is now back at its original state.
How is calcium used in muscle contraction?
Calcium binds to troponin, which moves the tropomyosin out of the way so that myosin can bind to actin; this ultimately causes a power-stroke.
How does troponin facilitate cross bridge formation?
Troponin controls the position of tropomyosin on the thin filament, enabling myosin heads to bind to the active sites on actin.
