Prokaryotic Gene regulation

The process of turning on a gene to produce RNA and protein is called gene expression. For a cell to function properly appropriate  proteins must be synthesized at the appropriate  time. Whether in a simple unicellular organism  or a complex multi-cellular organism, each cell controls  when and how its genes are expressed.

Prokaryotic organisms are single-celled organisms that lack a defined nucleus; therefore, their DNA floats freely within the cell cytoplasm. To synthesize a protein, the processes of transcription (DNA to RNA) and translation (RNA to protein) occur almost simultaneously. The expression of a gene is a highly regulated process and ensures that a cell’s resources are not wasted making proteins that the cell does not need at that time.

Prokaryotic transcription and translation occur simultaneously in the cytoplasm, and regulation occurs at the transcriptional level.

 Regulation of Gene expression  in Prokaryotes

Operons

In prokaryotes , genes with  related functions for example  the genes that encode the enzymes of a single biochemical pathway— are found next to each other on the DNA  or clustered together and  regulated together  . Such gene clusters  shares same promoter and a regulatory sequence  that controls the transcription of the entire unit. The organization of genes in this manner is called an OPERON.  This arrangement enables the prokaryote to rapidly adapt to changes in the environment.

Prokaryotic  mRNAs are Poly cistronic  , meaning they contain the information to make more than one protein. The promoter has simultaneous control over the regulation of the transcription of these structural genes.

The operon includes two main components namely

• Structural genes – genes that encode proteins used in metabolism or biosynthesis or that play a structural role in the cell and 
• Regulatory elements-  includes the promoter and the region surrounding the promoter and the genes that code for the regulatory proteins

In prokaryotic cells, there are three types of regulatory molecules that can affect the expression of operons namely ;

•  Repressors– are proteins that suppress transcription of a gene in response to an external stimulus,
• Activators – are proteins that increase the transcription of a gene in response to an external stimulus and
• Inducers – are small molecules that either activate or repress transcription depending on the needs of the cell and the availability of substrate.