section_path: Distinguishing features/Cytoskeletal structures
section_name: Cytoskeletal structures
paragraph_text: Cytoskeletal structures
  
  The cytoskeleton provides stiffening structure and points of attachment for motor structures that enable the cell to move, change shape, or transport materials. The motor structures are microfilaments of actin and actin-binding proteins, including α- actinin, fimbrin, and filamin are present in submembranous cortical layers and bundles. Motor proteins of microtubules, dynein and kinesin, and myosin of actin filaments, provide dynamic character of the network.
  
  Many eukaryotes have long slender motile cytoplasmic projections, called flagella, or multiple shorter structures called cilia. These organelles are variously involved in movement, feeding, and sensation. They are composed mainly of tubulin, and are entirely distinct from prokaryotic flagella. They are supported by a bundle of microtubules arising from a centriole, characteristically arranged as nine doublets surrounding two singlets. Flagella may have hairs (mastigonemes), as in many Stramenopiles. Their interior is continuous with the cell's cytoplasm.
  
  Centrioles are often present, even in cells and groups that do not have flagella, but conifers and flowering plants have neither. They generally occur in groups that give rise to various microtubular roots. These form a primary component of the cytoskeleton, and are often assembled over the course of several cell divisions, with one flagellum retained from the parent and the other derived from it. Centrioles produce the spindle during nuclear division.