Summary. It is known that DNA is described as a double helix, however if this double helix closes itself it is a knot. More generally, a double helix can be described as what mathematicians call braids with two strings. Closed braids give knots. The geometry of knots is not as simple as it looks and it might imply a physical complexity for the properties of the DNA.

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(*) Professor Le Dung Trang is Head of the Mathematics Section of the ICTP and previously was Director of Research at the French National Research Council as well as holding professorships in France at the University of Paris 7, Ecole Polytechnique and the University of Provence. His areas of expertise are the Theory of singularities, Algebraic Geometry, Differential Topology, Complex Dynamical Systems and Algebraic Differential Equations. His worldwide collaborations are with researchers from Paris, Boston, Munster, Nantes and Armenia. Besides he is regularly in contact with Vietnamese mathematicians in the capital, Hanoi, as well as in Dalat, in the Lam Dong Province. He is also in close contact Mexican mathematicians in Cuernavaca, Mexico. Elsewhere in the world he is collaborating in the development of post-graduate studies and research in Africa. For his many efforts and distinguished career he has been a Member of TWAS since 1993.