Biology · Support and Movement

Option B is correct since the myosin head binds to the ATP and adopts a high-energy configuration to bind to the myosin-binding site on the actin filaments. Option A is incorrect as actin does not involve the use of ATP itself. Rather, the highly energized myosin heads pull the actin filaments towards the M-line. Option C is incorrect since troponin is a regulatory protein bound to the tropomyosin to help it cover the myosin-binding sites on the actin filaments. When a nerve impulse arrives at the neuromuscular junction, the calcium ions released from the sarcoplasmic reticulum bind to the troponin molecules to move the tropomyosin, exposing the myosin-binding sites. (No ATP is involved with troponin directly). Option D is incorrect since tropomyosin is also a regulatory protein (an actomyosin complex inhibitor) that is also stimulated when the calcium ions bind to the troponin molecules upon the receive of nerve impulses. (No ATP is involved with troponin directly.)

A is incorrect, as actin does not involve the use of ATP itself. Rather, the highly energized myosin heads pull the actin filaments towards the M-line.

B is correct, since the myosin head binds to the ATP and adopts a high-energy configuration to bind to the myosin-binding site on the actin filaments.

C is incorrect since troponin is a regulatory protein bound to the tropomyosin to help it cover the myosin-binding sites on the actin filaments. When a nerve impulse arrives at the neuromuscular junction, the calcium ions released from the sarcoplasmic reticulum bind to the troponin molecules to move the tropomyosin, exposing the myosin-binding sites. (No ATP is involved with troponin directly.)

D is incorrect, since tropomyosin is also a regulatory protein (an actomyosin complex inhibitor) that is also stimulated when the calcium ions bind to the troponin molecules upon the receive of nerve impulses. (No ATP is involved with troponin directly.)