Final answer:
During muscle contraction, the protein myosin interacts with the protein actin, facilitated by the presence of calcium ions and regulated by the proteins troponin and tropomyosin. This interaction is part of the sliding filament model where muscle fibers contract as myosin and actin slide past each other.
Step-by-step explanation:
The two muscle components that interact during muscle contraction are the protein myosin and the protein actin. Myosin, which makes up the thick filaments, interlocks with the actin of thin filaments as it pulls the actin, causing the muscle to shorten or contract. This process is part of what's known as the sliding filament model of muscle contraction, where the actin and myosin slide past each other, leading to the shortening of muscle fibers and the generation of muscular force.
The interaction between myosin and actin is regulated by the presence of calcium ions (Ca++) and two other proteins, troponin and tropomyosin, which are part of the thin filaments. In the presence of Ca++, these regulatory proteins undergo a conformational change that exposes the binding sites on actin filaments, allowing myosin to form cross-bridges with actin. This calcium-triggered exposure is essential for muscle contraction to occur. Additionally, the binding of adenosine triphosphate (ATP) to myosin is crucial for the detachment and reattachment of the myosin head to the actin filament, which powers the contraction cycle.
Contraction continues as long as calcium ions remain present, allowing the actin-binding sites to be accessible. Relaxation occurs when calcium ions are removed, and tropomyosin re-blocks the binding sites on actin molecules, preventing interaction with myosin and causing the muscle fibers to lengthen back to their resting state.