This concentration is referred to as the critical concentration for assemble of polymer. This polarity can also be demonstrated by decorating actin with myosin heads, which decorate it in a shevron, or arrowhead pattern. Hence, the critical concentration is different at the two ends of the polymer. This non-equivalence of the two ends of the polymer means that there is a constant flux of subunits though polymer. By binding free actin monomer - which would otherwise be present at concentrations that vastly exceed C c , the cell can control actin polymerization.
Listeria binds to receptors on the cell surface, and is phagocytosed.
It then escapes from the phagosome, and is relelased free into the host cytoplasm. Therefore, the bacterium grows a tail of actin filaments, and that polymerization is sufficient to move the bacterim though the cytoplasm. The acrosomal process is a thin membrane-bounded process that grows off of a sperm cell to penetrate the vitelline coat that surrounds the egg. This reaction is dependent strictly on the polymerization of cytoplemic actin. This calcium binds to the profilin, causing a conformational change which inactivates it.