For instance most cells continually synthesize ribosomes and so have a continuous requirement for transcription of the rRNA and ribosomal protein genes. Genes that are active all the time are called housekeeping genes . On the other hand, many genes have more specialized roles and their biological information is needed by the cell only under certain circumstances. All organisms are therefore able to regulate expression of their genes, so that those genes whose RNA or protein products are not needed at a particular time are switched off. Overview of the basic features of gene regulation in bacteria and in eukaryotes.
Prokaryotes use transcriptional and translational-level control.
A. Gene regulation in E.coli Gene regulation enables a bacterium to respond to changes in the environment. An example is provided by those bacterial genes involved in utilization of different sugar compounds as sources of carbon and energy. E. coli possesses a number of genes coding for a variety of enzymes that enable the cell to take up and metabolize any of several different sugars. Which enzymes are actually made is determined by which sugars are available in the environment. This way, the bacterium doesn't waste energy making enzymes that don't have any available substrate.