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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.
Microfilaments, also called actin filaments, are protein filaments in the cytoplasm of eukaryotic cells that form part of the cytoskeleton. They are primarily composed of polymers of actin , but are modified by and interact with numerous other proteins in the cell.
Cytochalasin is a toxin that will bind to the actin polymer, so it can no longer bind to the incoming actin monomers. Actin originally attached in the polymer is still leaving the microfilament causing depolymerization. Phalloidin is a toxin that will bind to actin locking the filament in place. Monomers are neither adding or leaving this ...
By definition, the cytoskeleton is composed of proteins that can form longitudinal arrays (fibres) in all organisms. These filament forming proteins have been classified into 4 classes. Tubulin-like, actin-like, Walker A cytoskeletal ATPases (WACA-proteins), and intermediate filaments. [8] [28]
The actin filaments depolymerize and disassemble on the proximal end to allow free monomers to migrate to the leading edge (distal end) of the actin filament where it can polymerize and thus reattach. Actin filaments are also constantly being transported away from the leading edge by a myosin-motor driven process known as retrograde F-actin flow.
Actin filaments, present in the cytosol, are most abundant near the cell surface. These filaments are thought to determine the shape and movement of the plasma membrane. The nucleation of actin fibers occurs as a response to external stimuli, allowing a cell to alter its shape to suit a particular situation.
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 ...
Cofilin is a ubiquitous actin-binding factor required for the reorganization of actin filaments. ADF/Cofilin family members bind G-actin monomers and depolymerize actin filaments through two mechanisms: severing [11] and increasing the off-rate for actin monomers from the pointed end. [12] "Older" ADP/ADP-Pi actin filaments free of tropomyosin ...