Prokaryotic Gene Regulation

Art Connections

Figure In E. coli, the trp operon is on by default, while the lac operon is off. Why do you think that this is the case?


Figure Tryptophan is an amino acid essential for making proteins, so the cell always needs to have some on hand. However, if plenty of tryptophan is present, it is wasteful to make more, and the expression of the trp receptor is repressed. Lactose, a sugar found in milk, is not always available. It makes no sense to make the enzymes necessary to digest an energy source that is not available, so the lac operon is only turned on when lactose is present.