The Operon

The total amount of DNA present in a cell may contain from a few to thousand of genes. Although the different types of cells in the body of a multicellular organism differ in structure and function, their genes of a multicellular organism differ in structure and function, their genes are identical since all the cells are ultimately derived from the zygote. The problem therefore is: how do cells with identical genetic complements differ so much in structure and function? The answer is that not all genes are active at one time. As development proceeds certain genes become active while other become inactive, i.e., the genes are “switched on” and switched off” at different times. This process is called differential gene action. When genes are active they direct the formation of enzymes which affect certain traits. The metabolic product formed may repress synthesis of enzymes. Thus enzyme synthesis is induced and repressed at different times.

Although a cell has the genes to produce hundreds of enzymes, only the enzymes required at a particular time are produced. This control mechanism ensures that the cell is not flooded with unnecessary enzymes. The operon consists of the following components: regulator gene, promoter gene, operator gene, structural gene, repressor corepressor and inducer.