Final Answer:
The structure composed of protein filaments at the center of the thick filaments is called the M-line.
Step-by-step explanation:
Within the sarcomeres of muscle cells, the M-line serves as a crucial structural component located at the center of the thick filaments. Composed primarily of proteins like myomesin, the M-line provides stability and structural support by anchoring the thick filaments in place during muscle contraction.
This structure acts as a scaffold for organizing and stabilizing the arrangement of myosin, a major protein found in thick filaments. Myosin molecules attach to the M-line, helping to maintain the structural integrity of the sarcomere and ensuring proper alignment and functioning of the contractile proteins during muscle contraction.
The M-line's presence is essential for maintaining the overall structural integrity of the sarcomere and ensuring coordinated muscle movement. It plays a crucial role in regulating the interactions between thin and thick filaments, contributing significantly to the proper functioning of skeletal and cardiac muscle tissues.
Overall, the M-line's organization and composition of protein filaments are integral to the structural support and functioning of the sarcomere within muscle cells.