The cytoskeleton in eukaryotic cells defines the size and shape of a cell and is also closely related to mitosis, organization of the organelles within the cell, and intracellular transportation of vesicles. Actin filaments (F-actin) are the most abundant element of the cytoskeleton and are composed of the globular actin monomer (G-actin). Monomeric G-ATP (G-actin that is bound with ATP) polymerize both in vitro and in vivo to form F-actin in the presence of salt. The dynamics of the growth of F-actin are related to the generation of forces in the cell and cell locomotion. Therefore, a major goal of molecular biophysics is to understand how the structures and properties of G-actin generate the mechanics and dynamics of the actin filament.