microfilament

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

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