Anyone who has been on a sail boat knows that tying a knot is the best way to secure a rope to a hook and prevent slippage. Similarly, knots in sewing threads prevent them slipping through two pieces of fabric. How, then, can long DNA filaments, which have convoluted and highly knotted structure, manage to pass through the tiny pores of various biological systems? This is the fascinating question addressed by Antonio Suma and Cristian Micheletti, researchers at the International School for Advanced Studies (SISSA) in Trieste, who used computer simulations to investigate the dynamics of the molecule in such situations. The study has just been published in PNAS, the journal of the National Academy of Sciences of the Unites States.