The objective of this proposal is to combine different computational methods to study the physics of specific cellular components and processes which involve biological macromolecules. We will especially concentrate on the study of polyelectrolye DNA chains and analogous biopolymers and will investigate on their interaction with cellular structures and on the mechanisms of modifications of their physical properties. The understanding gained will allow us to explore different cellular processes related to gene delivery such as self-assembly of cationic lipid-DNA complexes and membrane fusion, relevant because of their fundamental properties as well as their applications in the biomedical sector. To achieve this goal, it is necessary to reach time and length scales in which macromolecules evolve, a regime that is out of reach of standard modelling approaches. To this end, we intend to adopt and refine a new chemically-aware coarse grained scheme and use complementary state of the art modelling techniques such as atomistic molecular dynamics and unspecific coarse graining. In addition, supercomputing techniques and resources will be exploited to provide unique scientific insights. The proposal will benefit from the expertise in biomolecular studies of scientists at the Barcelona Biomedical Park (PRBB), which will guarantee feedback and a cross-field perspective to the management of the project and to the production and interpretation of scientific results. This project is very relevant to the goals of the IEF activity of the people work programme because of its ingrained multidisciplinary character and because it directly targets key research areas indicated by the EU such as biotechnology and nanotechnology. The different training and research activities planned would increase and diversify the scientific competences of the fellow, leading him to a more independent and mature professional status on which to build his future career.