DNA is perhaps the most important of all biomolecules, not only because it carries the genetic information of biological systems, but also because of its mechanical flexibility that helps its biological function. Thus, elasticity of DNA plays an important role in its biological function. With a typical length of a few macrometers to several centimeters, it is only two nanometers wide. When the molecule is free in aquatic environment and in physiological conditions it behaves like a flexible rod, but the molecule is usually found in very tight geometries. In eukaryotic cells, it tightly fits inside micron-sized cell nuclei, with many sharp bends in nano scale. As another example, it can be encapsulated and found in highly confined structures in viral capsids with a size of tens of nanometers. Thus, understanding the structure of the molecule under such severe confinements and the way the molecule responds to these geometrical constraints, may help to understand DNA function better.
 
In this talk we overview the theoretical models and their results in molecular structure of DNA in nanoscale, and its mechanical response to external perturbations.