When a Sarcomere is at Rest,the Myosin Binding Sites on Actin

Question

When a sarcomere is at rest,the myosin binding sites on actin are blocked by _____.  
A) phosphorous
B) sodium
C) tropomyosin
D) the myosin heads
E) AMP

Accepted Answer

When a sarcomere is at rest, the myosin binding sites on actin are blocked by tropomyosin. Tropomyosin is a protein that lies in the groove of the actin filament and physically blocks the myosin head from binding to the actin filament. This blocking mechanism prevents any sliding of the actin and myosin filaments and results in muscle relaxation.