The Poland-Scheraga Model 8.334 Final Project

The Poland-Scheraga (PS) Model is one of the most celebrated applications of statistical physics to biology. By relying on basic laws of statistical phase transitions the PS model describes the denaturation of DNA strands as a function of temperature according to a minimal set of assumptions. The basic model makes the prediction of a second-order phase transition in the order parameter of the system (i.e. the fraction of the monomers which are bound to each other) in 3 dimensions, yet experimental observations suggest a first order transition. Thus an active area of research in the past few decades has involved complicating the PS model in such a way as to obtain the observed first-order phase transition. In this review, we describe the basic PS model and its successes/failures; then we extend the model in a novel direction, examining the effects of a term that suppresses long bound chains; finally we review a recent paper which describes how incorporating “excluded volume effects” into the model results in a first-order transition (in agreement with experiment).