Science series. An elegantly simple structure that resembles a twisted ladder-this is how the molecule that is the origin of life, DNA, has been described. One of its discoverers, Professor James Watson , talks to Quentin Cooper about how revealing the double-helix structure of this fascinating molecule in 1953 revolutionised our understanding of life and transformed his career as a 25-year-old biologist. Producer Fiona Roberts. E-MAIL: material.world@bbc.co.uk