Which of the following is the thin contractile protein?

Actin is the thin contractile protein found within muscle fibers. It plays a key role in muscle contraction by interacting with myosin, the thick contractile protein. During muscle contraction, actin filaments slide over myosin filaments, which allows for the shortening of the muscle. Actin is integral to the structure of the muscle cell and helps in the formation of the sarcomere, the functional unit of muscle contraction.

In addition to its role in contraction, actin is also involved in various cellular processes such as maintaining cell shape, cellular movement, and the transport of organelles within cells.

Myosin, while crucial for contraction, is classified as a thick protein, and proteins like tropomyosin and troponin serve more regulatory functions by controlling the interaction between actin and myosin, rather than acting as contractile proteins themselves.