Question

which of the following statements about muscle contractions are true?
true
drag appropriate answer(s) here
binding of myosin to actin is reversible.
they occur at the unit of the sarcomere.
z discs are pushed apart.
actin and myosin filaments run the length of the myofibril.
they rely on the sliding of actin and myosin filaments past one another.

Explanation:

• Binding of myosin to actin is reversible: During muscle contraction, myosin binds to actin to form cross - bridges. As the contraction cycle progresses (e.g., when ATP binds to myosin), the myosin - actin bond is broken, making the binding reversible.
• They occur at the unit of the sarcomere: The sarcomere is the basic unit of muscle contraction. It contains overlapping actin and myosin filaments, and the shortening of sarcomeres (due to the sliding of filaments) results in muscle contraction.
• They rely on the sliding of actin and myosin filaments past one another: This is the sliding - filament theory of muscle contraction. Myosin heads pull on actin filaments, causing them to slide over each other.
• Actin and myosin filaments run the length of the myofibril: Myofibrils are made up of repeating units (sarcomeres) which contain actin (thin) and myosin (thick) filaments that extend along the length of the myofibril.
• Z discs are pushed apart: This is false. During muscle contraction, Z discs (which mark the boundaries of a sarcomere) are pulled closer together as the sarcomere shortens.

Answer:

• Binding of myosin to actin is reversible.
• They occur at the unit of the sarcomere.
• They rely on the sliding of actin and myosin filaments past one another.
• Actin and myosin filaments run the length of the myofibril.