Explain lac operon with diagram.


An Operon is a coordinated group of genes which function together and regulate a metabolic pathway. Lac operon is lactose operon. It consists of 1 regulatory (inhibitory), 1 promoter, 1 operator and 3 structural genes. In E.coli, breakdown of lactose requires 3 enzymes. These enzymes are synthesized together by lac operon. The structural genes in lac operon are
1. lac z- coding for ß- galactosidase which breaks down lactose into galactose and glucose,
2. lac-y- coding for permease which increases permeability of cell to ß- galactosides,
3. lac a- coding for transacetylase, transfers acetyl group to ß- galactoside.

The operon is switched off when repressor protein produced by regulatory gene binds to operator gene.  RNA polymerase gets blocked and hence no transcription occurs. Therefore, lac operon is also referred to as negative control.  

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