Final answer:
Actin filaments, or microfilaments, are thin cytoskeletal structures composed of actin proteins. They have polarity and consist of two intertwined strands of actin monomers. Actin filaments play important roles in cell movement, muscle contraction, and maintaining cell shape.
Step-by-step explanation:
Actin filaments, also known as microfilaments, are thin cytoskeletal structures composed of actin proteins. They are 6 nm in diameter and consist of two intertwined strands of actin monomers. Actin filaments have polarity, with one end called the 'plus' end and the other end called the 'minus' end.
Before actin filaments repeat, they undergo a twisting motion. However, the exact number of twists before they repeat can vary. Actin filaments are primarily involved in cell movement, muscle contraction, maintenance of cell shape, and supporting the cell membrane.