Overview Examples actin Structure helical polymers of G-actin has polarity + end is site of formation - end is site of degradation "treadmilling" formation requires ATP dynamic structure that is constantly forming and breaking down can sample environment G-actin has intrinsic ATPase capabilities Function can interact with myosin to mediate contractile forces mediate motile forces mediate cytokinesis can interact with cell membrane to form core of microvilli function to increase absorptive surface area anchor tight junctions anchor zonula adherens