Question

Active sites on the actin filaments are exposed when the

• A. $M{g}^{+}$ ions bind with troponin
• B. $C{a}^{++}$ ions bind with tropomyosin
• C. $C{a}^{++}$ ions bind with troponin
• D. $M{g}^{++}$ ions bind with troponin

Answer 1

The correct option is C $C{a}^{++}$ ions bind with troponin

• When an electrical signal passes down the motor nerve to the muscle it causes the depolarisation of the muscle membrane.
• This triggers the release of calcium ions into the muscle interior where they bind to troponin.
• This causes the tropomyosin to shift from the face of the actin filament to which myosin heads needs to bind to produce contraction.
• Thus, the active sites on actin filaments are exposed.