The document discusses the cytoskeleton, which includes microtubules, microfilaments, and intermediate filaments that provide structure and shape to cells. Microtubules are involved in cell division and movement. They are assembled from tubulin and are dynamic, growing and shrinking rapidly. Microfilaments are composed of actin and are involved in cell motility, cytokinesis, and muscle contraction. Intermediate filaments provide mechanical strength and help define cell and tissue types. The cytoskeleton interacts with cellular structures like centrioles and the extracellular matrix to carry out essential functions in cells and tissues.