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Interactions between actin and myosin filaments of the sarcomere are responsible for what?
The interactions between actin and myosin filaments of the sarcomere are responsible for muscle contraction. Myosin heads bind to actin filaments, forming cross-bridges that pull the actin filaments towards the center of the sarcomere. This sliding action shortens the sarcomere, leading to muscle contraction.
When myosin cross bridges bind to actin what happens?
Muscle contraction results
What happens when calcium ions bind to troponin?
When calcium ions bind to troponin, it causes a conformational change in the troponin-tropomyosin complex, which exposes the binding sites on actin. This allows myosin to bind with actin and initiates the process of muscle contraction.
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.
The ability of myosin to interact with actin is regulated by the binding of?
The ability of myosin to interact with actin is regulated by the binding of calcium ions to troponin, which then allows tropomyosin to move away from the binding site on actin. This exposes the myosin-binding sites on actin, allowing myosin to bind and initiate muscle contraction.
What specific event triggers the uncovering of the myosin site on actin?
Calcium ions bind to troponin and change its shape.
How is calcium used in muscle contraction?
Calcium ions are essential for muscle contraction as they bind to the protein complex troponin, causing tropomyosin to move out of the way and expose the myosin-binding sites on actin. This allows the myosin heads to bind to actin and form cross-bridges, leading to muscle contraction. After contraction, calcium is pumped back into the sarcoplasmic reticulum to relax the muscle.
What is needed to attach and detach myosin heads from actin?
For attachment of myosin heads to actin, calcium ions must bind to troponin, causing tropomyosin to move out of the way, exposing the binding site on actin. ATP then binds to the myosin head, leading to its activation and attachment to actin. For detachment, ATP is hydrolyzed, causing a conformational change in the myosin head that releases it from actin.
How do cross bridge power stroke bring about shortening of muscle contraction in human?
During muscle contraction, the cross-bridge power stroke occurs when myosin heads bind to actin filaments and then pivot or "power stroke," pulling the actin filaments towards the center of the sarcomere. This action causes the muscle fibers to shorten, resulting in overall muscle 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.
Does Tropomyosin molecules move and expose specific sites on myosin filaments?
Yes, tropomyosin molecules block specific binding sites on actin filaments in relaxed muscle. When calcium ions bind to troponin, it causes a conformational change in tropomyosin, exposing the binding sites on actin, which allows myosin heads to bind and initiate muscle contraction.
