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Molecular & Cell Biology
S. Rahgozar,PhD
University of Isfahan
Faculty of Science
2. Cytoskeleton and Cell Movement
2.1. Actin Filaments
1389-90
Assembly and disassembly of actin filaments
Actin Filaments Actin monomer (G actin)
Barbed end
Pointed end
ADP-bound actin, which is
primarily at the pointed
end of the filament,
dissociates more readily
from the filament than
ATP-bound actin.
In contrast, actin bound to
ATP associates more
readily with the rapidly
growing barbed ends.
ATP binding and
hydrolysis play a key role
in the dynamic behavior of
actin filaments.
ADF/cofilin proteins bind to actin
filaments and enhance the rate of
dissociation of ADP-actin monomers
from the pointed end.
Profilin enhances the rate of
association of ATP-actin monomers
to the barbed ends.
1- ADF/cofilin and
Profilin
o Depolimerization/ polymerization
ADF/cofilin can sever actin
filaments.
ADF/cofilin binds to ADP-actin ,
severing the filaments and creating
new barbed and pointed ends.
o Filament severing
Association of actin filaments with the plasma
membrane
The network of actin
filaments and associated
actin-binding proteins is
called the cell cortex.
Cell cortex determines
cell shape and is
involved in a variety of
cell surface activities,
including movement.
Attachment of stress fibers to the plasma membrane
at focal adhesions
Stress fibers and
focal adhesions in a
cultured human
fibroblast
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