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microfilament





microfilament structure
Microfilament structure
A linear assemblage of the protein actin; microfilaments, also called actin filaments, are one of three main components of the cytoskeleton. Microfilaments serve a number of functions. They:
  • form a band just beneath the cell membrane that
    • provides mechanical strength to the cell
    • links transmembrane proteins (e.g., cell surface receptors) to cytoplasmic proteins
    • anchors the centrosomes at opposite poles of the cell during mitosis
    • pinches dividing animal cells apart during cytokinesis;
  • generate cytoplasmic streaming in some cells;
  • generate locomotion in cells such as some leukocytes (white blood cells) and the amoeba;
  • interact with myosin ("thick") filaments in skeletal muscle fibers to provide the force of muscular contraction.
The microfilament is a single-stranded helix with each monomer rotated 166° with respect to neighboring subunits; this means that every 36 nanometers, or every 13 subunits, subunits eclipse each other at what appears to be a crossover.

Because actin subunits have polarity, so also do the microfilaments from which they are built. Traditionally, the ends of a microfilament have been referred to as "pointed" and "barbed," a nomenclature that arises from the resemblance of microfilaments decorated with fragments of myosin II to arrowheads in the electron microscope.


Related category

   • CELL BIOLOGY