With skeletal muscle contraction, what prevent the development of cross-bridges between the actin and myosin? Select all that apply
A) Tropomyosin attaches globular heads to the myosin filament.
B) Troponin covers the tropomyosin-binding sites and prevents the formation of cross-bridges.
C) ATP actually plays a role in the positioning of the myosin filaments and actin.
D) The concentration of calcium around the myofibrils will prevent the cross-bridges from being formed.
Ans: A, B
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Associated with each actin filament are the two regulatory proteins: tropomyosin and troponin. Tropomyosin, which lies in grooves of the actin strand, provides the site for attachment of the globular heads of the myosin filament. In the noncontracted state, troponin covers the tropomyosin-binding sites and prevents formation of cross-bridges between the actin and myosin. Energy from ATP is used to break the actin and myosin cross-bridges, stopping the muscle contraction. The binding of calcium to troponin uncovers the tropomyosin-binding sites such that the myosin heads can attach and form cross-bridges.
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