Final answer:
Myosin is associated with actin filaments, also known as microfilaments, which are crucial for muscle contractions and other cellular movements.
Step-by-step explanation:
The motor protein myosin is associated with actin filaments. These actin filaments, also known as microfilaments, are composed of two intertwined strands of actin which provide the track along which myosin moves. This movement is powered by ATP hydrolysis. In muscle cells, myosin and actin filaments interact to enable muscle contractions. Myosin heads, which have ATPase activity, bind to actin filaments causing the muscle to contract through a series of allosteric changes.
In skeletal muscle, thick filaments made up of myosin pull on thin actin filaments during muscle contraction. Actin has specific binding sites for myosin attachment, which are blocked by tropomyosin when the muscle is at rest. This interaction between myosin and actin is crucial for muscle contraction as well for other cellular movements like cell division and cytoplasmic streaming.