Prokaryotic Gene Regulation

How are prokaryotic genes regulated?

As it turns out, bacteria and other prokaryotes do not need to transcribe all of their genes at the same time. To conserve energy and resources, prokaryotes regulate their activities, using only those genes necessary for the cell to function. For example, it would be wasteful for a bacterium to produce enzymes that are needed to make a molecule that is readily available from its environment. By regulating gene expression, bacteria can respond to changes in their environment—the presence or absence of nutrients, for example. How? DNA-binding proteins in prokaryotes regulate genes by controlling transcription. Some of these regulatory proteins help switch genes on, while others turn genes off.

How does an organism know when to turn a gene on or off? One of the keys to gene transcription in bacteria is the organization of genes into operons. An operon is a group of genes that are regulated together. The genes in an operon usually have related functions. E. coli, shown in Figure 13–15, provides us with a clear example. The 4288 genes that code for proteins in E. coli include a cluster of 3 genes that must be turned on together before the bacterium can use the sugar lactose as a food. These three lactose genes in E. coli are called the lac operon.

FIGURE 13–15 Small Cell, Many Genes This E. coli bacterium has been treated with an enzyme enabling its DNA, which contains more than 4000 genes, to spill out.