Explain the Iac-operon of E.coli with the help of schematic representation.

Explanation

1. Lac-opern,in bacteria a transcriptionally regulated system was proposed hy Jacob and Monod. The polycistronic structural genes are regulated by a common promoter and regulatory genes.

2. Three structual genes z, y, a, z-code for beta-galactosidase which hydrolyse lactose into galactose and glucosez-y-gene code for permease which increases permeability of the cell to lactose and the a-gene code for transacetylase:
3. Presence of lactose in the cell, regulates switching on or off of the operon and is termed inducer.
4. Repressor protein synthesised by i-gene. combine with induced (lactose) to form inactive repressor which does not bind to operator gene and RNA polymerase from promoter gene moves.to the structural genes to helpin.transcription. It the absence of lactose, represser binds to the operator gene whichis switched off and RNA polymerase cannot move from promotergene and thus there is no transcription. Regulation of lac operon by repressor is called negative regulation.
Note. The repressor of operon from i-gene is synthesised all the time, hence, i-gene is a constitutive gene: