Illustration of the US chemical engineer Frances Arnold (born 1956). Arnold is best known for her pioneering work that uses directed evolution to improve or give new properties to enzymes (proteins that drive chemical reactions). Arnold introduced different mutations into genes for the enzyme subtilisin and inserted the genes into bacterial cells. The bacteria produced the mutated enzymes, which Arnold then screened for the desired property. The genes for the most promising enzymes were put through this process again and again until the desired property was achieved. This process has been used to create numerous enzymes. Arnold has used directed evolution to create enzymes that can produce biofuel and that are environmentally-friendly replacements in the synthesis of industrial chemicals. She was awarded a share of the 2018 Nobel Prize in Physics for her work on directed evolution along with George Smith and Gregory Winter.