In order for high force crossbridges to form in contracting skeletal muscle, calcium must a. bind to calmodulin to phosphorylate the myosin. b. phosphorylate the tropomyosin which moves it. c. phosphorylate the troponin to move the tropomyosin. d. bind to tropomyosin which moves the troponin. e. bind to troponin which moves the tropomyosin.

e. bind to troponin which moves the tropomyosin.

Explanation:

Troponin (Tn) is a protein complex composed of three different proteins: troponin C (TnC), troponin I (TnI), and troponin T (TnT). This complex is found both in skeletal muscles and cardiac muscles, where TnC attaches calcium ions through four and three calcium ion-binding sites, respectively. When a muscle is relaxed, Tn attaches to tropomyosin to prevent muscle contraction. During muscle contraction, calcium channels open and cytosolic calcium ions bind to TnC, thereby Tn changes its conformation and moves the tropomyosin. This process relieves the inhibition of the interaction between actin and myosin filaments, which makes muscle contraction possible.

b a mature ovary of a plant.

not: both offer magnification to the atomic level.