Cell surface shape & movement. Actin filaments and microtubules are composed of globular subunits
Microtubules
Intracellular transport, positioning of organelles
Intermediate filaments
Mechanical strength. Composed of elongated and fibrous subunits. Resistant to tearing
Protofilaments
Long linear strings of filament subunits joined end to end
Nucleation
Multiple subunit-subunit contacts lead to rapid elongation by addition of more subunits
Critical concentration
Concentration at which monomeric subunits are in equilibrium with polymer. Here, rate of subunit addition=rate of subunit loss
Treadmilling
Polymer maintains a constant length, even though there is a net flux of subunits through the polymer. Happens at an intermediate subunit concetration, where growth of plus end is equal to shrinkage at minus end
