Final answer:
The two ends of an actin filament are known as the pointed (-) end and the barbed (+) end. Actin filaments, which feature in both skeletal and smooth muscle contraction, are essential for the sarcomere's contraction by interacting with the myosin motor protein. This polarity is crucial for the directional movement and the activity of ATPase during contraction.
Step-by-step explanation:
The two ends of an actin filament are referred to as the pointed (-) end and the barbed (+) end. In the context of muscle contraction, the interaction between actin and myosin is crucial. Actin filaments are integral to the structure of muscle fibers and play a pivotal role in muscle contraction by working together with myosin, a motor protein. During contraction, myosin heads bind to actin, pulling the thin actin filaments towards each other, which brings the Z-lines closer together, effectively shortening the sarcomeres - the basic units of muscle fibers.
Actin filaments are part of the cytoskeleton and consist of two intertwined strands of globular proteins, and their polarization with a plus and minus end is vital for the directional movement of myosin during contraction. The myosin heads specifically bind to the barbed (+) end, which allows the actin filaments to demonstrate a maximum rate of ATPase activity, essential for muscle contraction. Notably, these findings align with what is observed in the 'arrowhead pattern' seen when S1 myosin heads bind to the actin filaments during muscle contraction studies.