Cells are not just small test tubes, but present a mechanically complex, ever fluctuating environment in which essential biological processes take place. We investigate how the complex nanomechanical environment of the cell affects the dynamic motion of DNA. We compare single-molecule measurements with optical tweezers on DNA in vitro  with single-molecule particle tracking and fluorescence correlation spectroscopy experiments in living cells. Key findings are that (i) constraints on the DNA significantly affect its entropic elasticity, (ii) non-thermal fluctuations from active processes in living cells contribute significantly to the ability of DNA to move and form large regulatory co-complexes with proteins.