Originally posted by wormer
Concentration of actin in cells is 50-100 times greater than the critical concentration observed for pure actin in a test tube. How is this possible? What prevents the actin sub units in the cells from polymerizing into filaments? Why is it good for the cells to have such large sub units of actin?
Actin filaments in cells are highly dynamic. They undergo polymerization and depolymerization simultaneously through a variety of mechanisms. This process is used to drive processes like cell motility, shape, transport, contraction, etc. High actin concentrations permit the rapid growth and contraction of filaments. Actin filaments can also be stabilized with "capping" proteins to stop polymerization and maintain cell shape. As usual with most cell biology, there are lots of other proteins/molecules that can drive/interfere with the rate of growth/decay of the filaments. Phalloidin, the deadly ingredient from the death cap mushroom, works by binding between individual actin polymers in filaments and preventing their depolymerization.