Microfilaments (Actin Filaments)


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A structural role of microfilaments. The surface area of this nutrient-absorbing intestinal cell is increased by its many microvilli (singular, microvillus), cellular extensions reinforced by bundles of microfilaments. These actin filaments are anchored to a network of intermediate filaments (TEM).

Source: Urry, Lisa A.. Campbell Biology (p. 116). Pearson Education. Kindle Edition.

Microfilaments: Actin Filaments (Campbell Biology)

Microfilaments are thin solid rods. They are also called actin filaments because they are built from molecules of actin, a globular protein. A microfilament is a twisted double chain of actin subunits. Besides occurring as linear filaments, microfilaments can form structural networks when certain proteins bind along the side of such a filament and allow a new filament to extend as a branch. Like microtubules, microfilaments seem to be present in all eukaryotic cells.

In contrast to the compression-resisting role of microtubules, the structural role of microfilaments in the cytoskeleton is to bear tension (pulling forces). A three-dimensional network formed by microfilaments just inside the plasma membrane (cortical microfilaments) helps support the cell’s shape. This network gives the outer cytoplasmic layer of a cell, called the cortex, the semisolid consistency of a gel, in contrast with the more fluid state of the interior cytoplasm. In some kinds of animal cells, such as nutrient-absorbing intestinal cells, bundles of microfilaments make up the core of microvilli, delicate projections that increase the cell’s surface area.

Microfilaments are well known for their role in cell motility. Thousands of actin filaments and thicker filaments made of a protein called myosin interact to cause contraction of muscle cells. In the unicellular eukaryote Amoeba and some of our white blood cells, localized contractions brought about by actin and myosin are involved in the amoeboid (crawling) movement of the cells. The cell crawls along a surface by extending cellular extensions called pseudopodia (from the Greek pseudes, false, and pod, foot) and moving toward them. In plant cells, actin-protein interactions contribute to cytoplasmic streaming, a circular flow of cytoplasm within cells. This movement, which is especially common in large plant cells, speeds the movement of organelles and the distribution of materials within the cell.

Source:

Urry, Lisa A.. Campbell Biology. Pearson Education. Kindle Edition. https://www.pearson.com/us/higher-education/series/Campbell-Biology-Series/2244849.html

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