Free-energy depolymerization-polymerization

In the case of polymerization of G-ATP-actin, the ratio of the rates of association and dissociation of monomers is different at two ends. The critical concentration of G-ATP-actin is defined by the condition that the sum of the growth rates at the two ends and the sum of the depolymerization rates are equal. At one of the two ends, the depolymerization may be faster than the growth and at the other end, the growth may be faster. Then a cycling of actin monomers takes place from one end of F-actin to the free monomer to the other end. This phenomenon was named tread-milling [27]. As a result, the polymer translates. Consumption of the free energy of ATP hydrolysis is required for such unidirectional translation of F-actin. The coupling of the polymerization with an irreversible chemical reaction produces a dynamic function of the polymer. 

Actin and tubulin polymerization and depolymerization can generate mechanical forces using the free energy of monomer binding and/or nucleotide hydrolysis as their energy source. 

The free-energy change of depolymerization-polymerization AG is given by the reaction isotherm... 

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