Escherichia coli is a bacteria species that is able to break down lactose, a complex sugar found in milk. When lactose enters the cell through passive
transport, a repressor chemical is removed from a section of the DNA and
multiple proteins are synthesized. One type of protein embeds in the cell
membrane to facilitate the transport of high volumes of lactose into the cell.
Another protein plays the role of an enzyme that breaks down lactose into
two simple sugars, glucose and galactose. When the amount of lactose in
the cell decreases, the repressor chemical binds to the DNA again to block
the production of proteins.
Which step in the process best represents the regulation of gene expression
in Escherichia coli?