Free energy of twisted semiflexible polymers.
We investigate the role of fluctuations in single-molecule measurements of torque-link (t-lk) curves. For semiflexible polymers of finite persistence length (i.e., polymers with contour length L comparable to the persistence length LP), the torque versus link curve in the constant-torque (isotorque) ensemble is distinct from the one in the constant-link (isolink) ensemble. Thus, one encounters the conceptually interesting issue of a "free energy of transition" in switching ensembles while making torque-link measurements. We predict the dependence on the semiflexibility parameter beta=L/LP of this extra contribution to the free energy, which shows up as an area in the torque-link plane. This can be tested against future torque-link experiments with single biopolymers. We bring out the inequivalence of torque-link curves for a stiff polymer and present explicit analytical expressions for the distinct torque-link relations in the two ensembles and the free-energy difference in switching ensembles in this context. The predictions of our work can be tested against single-molecule experiments on torsionally constrained biopolymers.
Sinha
Supurna
S
Raman Research Institute, Bangalore, India. supurna@rri.res.in
D001703:Biophysics / Q000379:methods*; D001704:Biopolymers / Q000737:chemistry*; D003198:Computer Simulation; D005786:Gene Expression Regulation; D008956:Models, Chemical; D015233:Models, Statistical; D008962:Models, Theoretical; D011108:Polymers / Q000737:chemistry*; D015203:Reproducibility of Results; D013314:Stress, Mechanical; D013816:Thermodynamics
D001704:Biopolymers; D011108:Polymers