What do the thin protein fibers made of actin primarily contribute to in cells?

Thin protein fibers made of actin, known as microfilaments, play a crucial role in maintaining cell structure and facilitating cell motility. These actin filaments are integral components of the cytoskeleton, which provides the cell with its shape and mechanical support. They enable various forms of movement, including muscle contraction and cell division, and they are essential for processes like amoeboid movement seen in some eukaryotic cells.

Moreover, actin filaments interact with myosin, another protein, to create contractions that contribute to the mobility of cells. This process is vital for many cellular functions where movement is required, such as during wound healing or immune responses.

In addition to facilitating movement, actin filaments assist in the formation of cell junctions and are involved in determining the overall shape of the cell, allowing it to adapt and respond to its environment. Thus, the primary contribution of these thin protein fibers made of actin relates directly to the cell's ability to move and maintain its shape.