Question

When muscles contracts

• A. Sarcomeres increase in size
• B. Myosin slides past actin
• C. H zone disappears
• D. Calcium is taken up by calcium storage sacs

Answer 1

Answer: (C)

H zone disappears

• Myofibril activity is required for muscle contraction on the molecular level.
  
• When ATP binds to myosin, it separates from the actin of the myofibril, which causes a contraction.
• H zone disappears and Z zone moves towards each other.
• The muscle contraction cycle is triggered by calcium ions binding to the protein complex troponin, exposing the active-binding sites on the actin.
• ATP then binds to myosin, moving the myosin to its high-energy state, releasing the myosin head from the actin active site.
• So, the correct option is 'H zone disappears'.