{"type":"root","children":[{"type":"paragraph","children":[{"type":"text","value":"Actin is a globular-structural, 345 kDa protein that polymerizes in a helical fashion to form an actin filament (or microfilament). Actin filaments provide mechanical support for the cell, determine the cell shape, and enable cell movements through lamellipodia, filopodia, or pseudopodia. Actin also participates in certain cell junctions, cytoplasmic streaming and contraction of the cell during cytokinesis. In muscle cells, actin plays an essential role, along with myosin, to enable muscle contraction. In the cytosol, actin is predominantly bound to ATP, but can also bind to ADP."}]}]}