MICROANATOMY

Detailed explanation-1: -A complex protein called troponin is found on tropomyosin at regular intervals. During the resting stage, this protein masks the active binding sites of actin. When the calcium ions get released into the sarcoplasm it binds with the troponin and causes the active sites of actin to open for myosin.

Detailed explanation-2: -In the resting state, a subunit of troponin masks the active binding sites for myosin on the actin filaments.

Detailed explanation-3: -So, the correct option is ‘Tropomyosin’.

Detailed explanation-4: -Ca++ ions bind with a unit of troponin which is responsible for masking of active sites for myosin through tropomyosin. The event initiates cross-bridge activity during muscle contraction mechanism.

Detailed explanation-5: -Calcium ions rise, and troponin subunits on actin filaments bind to them. They remove the masking site for myosin filaments by binding, and by doing so, they need energy from ATP hydrolysis to do so.