Actin is a polymer made up of subunits.
An actin filament can gain or lose monomers
at either end, but with very different kinetics
The filaments can associate with one another under
the action of actin-binding proteins such as alpha actinin.
Using biological parameters such as actin-binding protein
association rates, k+ and k-, it is possible to estimate an
overall filament association rate. See Spiros and
Edelstein-Keshet (1998).
Filament length is controlled not only by polymerization,
but also by proteins that chop up the filaments.
A particularly interesting filament chopper is gelsolin,
whose influence on the actin filament length distribution was
investigated by Ermentrout and Edelstein-Keshet.