Force Generation by Cellular Polymers

1. Actin and tubulin polymerization and depolymerization can generate mechanical forces using the free energy of monomer binding and/or nucleotide hydrolysis as their energy source. 2. Polymers can also store elastic energy during their polymerization that can be released later to generate mechanical forces that drive some of the most rapid of cellular motions. 3. Actin and tubulin are tracks for walking motors powered by nucleotide hydrolysis. These motors fall into three classes: myosins, kinesins, and dyneins. The plural applies because, while the force generating principle within each motor type is the same, there is substantial diversity in their dynamical behavior and the cargo they propel. However, the polymer tracks themselves probably play only a passive role as highways for intracellular transport.