Regulation of gene expression

Regulation of gene expression means controlling the amount and time of formation of gene products according to the requirement of the cell.

• Gene expression can be regulated:
  -During transcription (transcriptional control).
  -During translation (translational control).
  -After translation (post-translational control).

THE LAC OPERON’

An operon is a unit of prokaryotic gene expression which includes coordinately regulated (structural gene) and control elements which are recognized by regulatory gene product.

COMPONENTS OF OPERON

1. Promoter:- The sequence of DNA where RNA polymerase binds and initiates transcription of structural gene is called Promoter.

2. Operator :– The sequence of DNA adjacent to promoter where specific repressor protein binds is called operator.

3. Regulatory gene :- The gene that codes for the repressor protein that binds to the operator and suppresses its activity as a result of which transcription will be switched off (i gene).

4. Structural gene :- The fragment of DNA which transcribe mRNA for polypeptide synthesise. There are three structural gene in Lac operon (Z, y, a).

5.Inducer :- The substrate that prevents the repressor from binding to the operator, is called an inducer.

Function Of Lac Operon

• Repressor is synthesized by I gene and it is functional all the time.
• Repressor binds to the operator of Lac operon.
• RNA polymerase is prevented from transcribing the template strand of DNA.=
• Lactose is used as a inducer in lac operon.
• Gene z codes for B-galactosidase breaks lactose down transacetylase aid in the metabolic process.

When lactose is present

When lactose are present in the cell, it will bind to sites on the repressor protein, changing its conformation and rendering it inactive. As the repressor protein detaches from the operator, RNA polymerase can bind to the promoter, transcription can occur, and the three lactose degradation genes can be synthesized.