On Start the Week Andrew Marr talks to Peter Wothers about modern day alchemy, as we enter a new era of chemistry. In the past some scientists dismissed the vast majority of the human genome as 'junk DNA', Ewan Birney argues for renaming it 'enigmatic DNA'. And curiosity gets the better of Sanjeev Gupta as he explores the terrain on Mars. But science doesn't have all the answers as Helen Bynum charts the history of tuberculosis, from the medieval period to the present day, and looks at how this killer disease continues to spread and evolve. Producer: Katy Hickman.