HOW SCIENTISTS REALLY REASON: SCIENTIFIC REASONING IN REAL-WORLD LABORATORIES

In 1965 Jacques Monod and François Jacob were awarded the Nobel prize for discovering that there are regulator genes that control the activity of other genes. They discovered this by investigating the utilization of energy sources, such as glucose, in E. coli. E. coli need glucose to live and their most common source of glucose is lactose. When lactose is present, E. coli secrete betagalactosidase enzymes that break down lactose into glucose. Betagalactosidase is secreted only when lactose is present. Jacob and Monod discovered that a set of regulator genes inhibit the genes that produce betagalactosidase until betagalactosidase is needed. They proposed that there are two genes I and O that regulate the activity of the betagalactosidase producing genes and that the production of beta-gal is controlled by an inhibitory regulation mechanism. As can be seen from Figure 1, when no lactose is present the I gene produces an inhibitor that binds to the O gene, and this prevents the betagalactosidase genes from producing betagalactosidase. When Lactose is present, the inhibitor secreted by the I gene binds to the lactose, rather than the O gene. When this happens, the betagalactosidase genes are no longer inhibited and, consequently, they produce betagalactosidase. When all the lactose is used, the inhibitor again binds to the O gene and production of betagalactosidase stops. Monod and Jacob made this discovery using various mutations where the I, O, and betagalactosidase genes were mutated. Crucially, they initially thought that genetic control was due to genes switching on, or activating, other genes. It was only after a large amount of research that they discovered that the mechanism of control was inhibition. Not only was this discovery relevant to production of betagalactosidase, but it was a general model of genetic control that transformed biological research.