At Rest, Active Sites on the Actin are Blocked By

Question

At rest, active sites on the actin are blocked by
A) myosin molecules.
B) troponin molecules.
C) tropomyosin molecules.
D) calcium ions.
E) ATP molecules.

Accepted Answer

At rest, the active sites on actin are blocked by tropomyosin molecules. These tropomyosin molecules are held in place by troponin molecules, which are regulated by calcium ions. When calcium binds to troponin, it causes a conformational change that moves the tropomyosin molecules out of the way, allowing myosin to bind to the actin active sites and initiate muscle contraction. ATP molecules are not involved in the blocking of the active sites on actin at rest.