Mesoscopic Models of Polymers: Semi-flexible Chains and Polyelectrolytes

Most biopolymers are semi-flexible: they can bend and undulate. Mechanically they are characterized by finite values of their persistence lengths \( l_{p} \), the scales below which the chains can be regarded as straight (Fig. 11.1). For example, the persistence length of double-stranded DNA is about 50 nm, while that of actin filament is about 20 μm. For the length scale much longer than the persistence length, the chain appears to be flexible, to which the models presented earlier can be applied. This chapter covers basic mesoscopic conformations, their fluctuations, and elastic behaviors of semi-flexible chains and polyelectrolytes that are either free or subject to external forces and constraints.