• Also called actin filaments • Thin solid rods • Built from actin, a globular protein • Twisted double chain of actin subunits • Occur as linear filaments and structural networks → Protein can bind along side of filament and let another filament extend as a branch

• Bear tension, pulling forces • 3-D network just inside plasma membrane helps support cell shape – Network is called cortical microfilaments – Gives cell cortex (outer cytoplasmic layer of cell) more of a gel consistency – Inside is more fluid • Bundles of microfilaments make up core of microvilli • Used with the protein myosin in cell motility and muscle contraction ← Amoebas and white blood cells use them to crawl (with pseudopodia)