Actin is a protein that plays a crucial role in the structure and movement of cells. It forms long, thin filaments that help maintain the cell's shape and support various cellular functions. Actin is found in all eukaryotic cells, which include plants, animals, and fungi, making it essential for life. In addition to providing structure, actin is involved in muscle contraction and cell movement. When muscles contract, actin filaments slide past each other, allowing the muscle to shorten and generate force. This process is vital for activities like walking, running, and even the beating of the heart, showcasing the importance of actin in our daily lives.