Final answer:
An actin filament is a double-stranded structure with two helical grooves. Made of intertwined strands of actin, it works with myosin to enable muscle contraction and other cellular movements.
Step-by-step explanation:
An actin filament (or F-actin, microfilament) is a double-stranded structure with two helical grooves running along its length. Microfilaments are essential components of the cytoskeleton in eukaryotic cells and play a crucial role in cellular processes such as muscle contraction. Constructed from two intertwined strands of actin, these filaments are about 7 nm in diameter and, when coupled with motor proteins like myosin, facilitate motion, including muscle contraction and the amoeboid movement of certain eukaryotic microbes.
Actin exists in either a polymerized gel form, which provides stability, or an unpolymerized soluble form. The polymerization and depolymerization of actin, powered by ATP, allow microfilaments to adapt and function dynamically within the cell. The interaction between actin and myosin, especially in muscle cells, is central to the process of muscle contraction whereby myosin filaments 'pull' on the actin strands.