Unzipping force

Figure 2. A directed polymer with an unzipping force.

If we consider the response of a directed polymer to the unzipping force, the response function comes from the Hamiltonian... 

It has been argued that the unzipping transition for the quenched averaged RANI case is second order [41]. However for real DNA, it is not the quenched averages that matter. There is strong ensemble dependence and sample to sample variation. This has been exploited to identify point mutants by a comparison of the unzipping force in a fixed distance ensemble [42]. An experimental determination of the unzipping phase boundary for a real DNA has been reported in Ref. [43]... 

Therefore, theorists can only estimate values of the parameters and use them for the calculations and analysis. Precise values, however, might come from experimental research. The last decade of the twentieth century will be remembered for the first successful experiments done on a single DNA molecule. This revolution in molecular biology started in 1996 [42,43]. Authors stretched the single DNA molecule and measured the applied force. In addition, the force that can unzip the strings of the DNA was measured [44-46]. Beside this progress, the values of the parameters are still unknown. Hopefully, the biophysical revolution is still in progress and keeps us in an optimistic mode. 

Unzipping DNA. The two strands separate, exposing two complementary copies of single-stranded DNA. They are forced apart by DNA helicase at the replication fork. 

D. J. Muller, W. Baumeister, and A. Engel, Controlled unzipping of a bacterial surface layer with atomic force microscopy, Proc. Natl. Acad Sci. USA,96,13170-13174(1999). 

Delocalization may arise as a result of the action of an external force. This is motivated by several real experiences, we mention in particular some recent experiments on mechanically induced unbinding (or unzipping) of a double strand of DNA via experiments at a molecular level (see Section 1.10 for literature and further details). From the arguments in Section 1.4 it is clear that we can directly look at the reduced model of pulling a polymer out of an attractive defect line. The model is the following ... 

For force induced unzipping or delocalization in model systems, but motivated by biopolymer experiments, we signal [Marenduzzo et al. (2001)] and [Lubensky and D. R. Nelson (2000)], even if our approach is rather different. An example of application of the same models outside of the biopolymer context can be found in [Kafri et al. (2006)]. Formula (1.41) extends easily to disordered cases, see [Giacomin (2004), Ex. 2.3] and from it a number of conclusions can be easily drawn. 

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