Exemplar Problems

Question 4

How does the interaction between actin and myosin contribute to muscle contraction?

Solution: The interaction between actin and myosin is central to muscle contraction. This interaction occurs when calcium ions, released from the sarcoplasmic reticulum, bind to troponin on the actin filaments. This binding causes a conformational change in troponin, which moves tropomyosin away from the actin’s myosin-binding sites. Myosin heads, energized by ATP, then bind to these exposed sites on actin, forming cross-bridges. Through a process called the power stroke, the myosin heads pivot, pulling the actin filaments toward the center of the sarcomere, thus shortening the muscle fiber and causing contraction.