EXTRA SEMINAR: Topology and statistical properties of polymers using DNA with an application to gene expression control

DNA is a very handy polymer because of its long persistence length that permits to study it over a large length scale from few nanometers up to micrometers, spanning from the stiff polymer regime up to the flexible regime. Moreover, DNA comes in different topological forms (linear, circular and knotted) therefore enabling to study the physics of polymers depending upon the topology of the investigated polymer. Moreover, concentrated "solution" in 2D and confined configurations can be investigated. For these studies, Atomic Force Microscopy (AFM) images of DNA were taken and analyzed using polymer physics concepts. It turns out that AFM images deliver a wealth of detailed data never available before and that now it allows additional comparison between theoretical predictions for linear, circular and knotted polymers with real polymers. One application of these studies to a biological problem consists in investigating the role of the degree of supercoiling of circular DNA in the control of gene expression.