Question

Describe the operon in bacterial DNA and explain the purpose of aligning certain genes back to back.

Answer 1

The main feature of operon is the arrangement of several structural genes under one common promoter and it is under regulation of a single operator. Because of this arrangement all the genes will be transcribed into a single mRNA (polycistronic mRNA) and will go for translation together.

It is predominantly observed in prokaryotes, but some eukaryotes are also known to have this system.

Examples are

Lac operon: here in E.coli, this operon has three structural genes along with promoter, terminator and operator.

This will be activated only when the substrate lactose is available (allolactose is the activator).

Trp operon: Here five structural genes: trp E, trp D, trp C, trp B, and trp A will encode tryptophan synthetase when there is an availability of tryptophan in the media. So when tryptophan is there it will repress the gene transcription.

Significance: Being simple organisms, these prokaryotes have adopted this operon system to synthesize enzymes when there is an actual need for it. And by producing polycistronic mRNA which encodes all the enzymes together needed for a particular process, the efficiency of the system will increase and wastage of machinery can be minimized.