Question

Which of the following answers describes the most direct consequence of tropomyosin binding to F-actin in muscle cells?

The (-) end of F-actin is stabilized

Loss of actin-ADP subunits from the (+) end is prevented

Myosin binding to F-actin is blocked

ATP hydrolysis by myosin is blocked
The movement of myosin towards the (+) end is blocked

Answer 1

The binding of tropomyosin to F-actin in muscle cells directly blocks myosin from binding to actin, preventing muscle contraction. The action of tropomyosin is regulated by the binding of calcium to troponin, leading to exposure of myosin-binding sites on actin for cross-bridge formation essential for muscle contraction. Option C

Step-by-step explanation:

The most direct consequence of tropomyosin binding to F-actin in muscle cells is that myosin binding to F-actin is blocked. When the muscle is at rest, tropomyosin covers the myosin-binding sites on the actin filament, preventing the formation of cross-bridges between actin and myosin filaments which are necessary for muscle contraction. The lifting of tropomyosin's blockade is regulated by calcium ions that bind to troponin, leading to a conformational change in the troponin-tropomyosin complex, thus exposing the myosin-binding sites on actin.

Upon exposure to calcium ions, troponin undergoes a change that moves tropomyosin away from the binding sites on the actin strands, allowing the myosin heads to create cross-bridges. These cross-bridges enable the myosin heads to perform a power stroke by pulling the thin filaments toward the center of the sarcomere, leading to muscle contraction. ATP is then required to release the myosin head from actin, enabling the cycle of contraction to continue. Option C

Answer 2

\rMyosin binding to F-actin is blocked

Step-by-step explanation:

Tropomyosin is a protein involved in skeletal muscle contraction and that wraps around actin and prevents myosin from grabbing it. This prevents muscle contractions until the proper signal arrives. When the nervous system tells the muscle cell to contract, calcium is released.