Once synthesized and folded, new proteins need to reach their final destination within the cell, amongst the other billions of protein molecules, constantly being synthesized and degraded. Some proteins may need to pass through one or two membrane barriers before reaching the site where they fulfll their function. In 1971, Günter Blobel and David Sabatini from the Rockerfeller Institute in New York suggested a ‘signal hypothesis’, in which proteins were given a luggage label, or zip code, to ensure they finished up in the right destination. Labelling takes the form of short sequences of amino acids, known as topogenic signals, which then attach to receptor proteins to allow them through membrane barriers to reach the correct destination. In 1999, Günter Blobel received the Nobel Prize for this work, which has explained the molecular mechanisms behind several diseases. Both cystic fibrosis and primary hyperoxaluria (a condition causing kidney stones at an early age) are caused by proteins failing to reach their correct destination. Blobel donated the million dollar prize money to the post-war reconstruction in Dresden, Germany, the country of his birth.