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Actin is a family of globular multi-functional proteins that form microfilaments in the cytoskeleton, and the thin filaments in muscle fibrils.It is found in essentially all eukaryotic cells, where it may be present at a concentration of over 100 μM; its mass is roughly 42 kDa, with a diameter of 4 to 7 nm.
Actin filaments are assembled in two general types of structures: bundles and networks. Bundles can be composed of polar filament arrays, in which all barbed ends point to the same end of the bundle, or non-polar arrays, where the barbed ends point towards both ends.
These filaments are made of two strands of actin monomers (or protofilaments) wrapping around each other, to create a single actin filament. Because actin monomers are not symmetrical molecules, their filaments have polarity based upon the structure of the actin monomer, which will allow one end of the actin filament to polymerize faster than ...
Intermediate filaments are part of the cytoskeleton structure found in most eukaryotic cells. An example of an intermediate filament is a Neurofilament . They provide support for the structure of the axon and are a major part of the cytoskeleton.
The thick filament, myosin, has a double-headed structure, with the heads positioned at opposite ends of the molecule. During muscle contraction, the heads of the myosin filaments attach to oppositely oriented thin filaments, actin, and pull them past one another. The action of myosin attachment and actin movement results in sarcomere shortening.
Thick filaments consist primarily of the protein myosin, that is responsible for force generation. It is composed of a globular head with both ATP and actin binding sites, and a long tail involved in its polymerization into myosin filaments. Elastic filaments are made up of a giant protein called titin and hold the thick filaments in place.
Two of its subunits, the Actin-Related Proteins ARP2 and ARP3, closely resemble the structure of monomeric actin and serve as nucleation sites for new actin filaments. The complex binds to the sides of existing ("mother") filaments and initiates growth of a new ("daughter") filament at a distinctive 70-degree angle from the mother.
In non-muscle cells, it is found by the actin filaments and at the adhesion sites. [1] The lattice like arrangement provides stability to the muscle contractile apparatus. [1] Specifically, it helps bind actin filaments to the cell membrane. [2] There is a binding site at each end of the rod and with bundles of actin filaments. [1]