Lac Operon|| Gene Regulation|| Chromosome and DNA|| Class 12

The lac operon is a genetic system in Escherichia coli (E. coli) and some other bacteria that controls the metabolism of lactose. It consists of a group of genes regulated together to enable the bacteria to use lactose as an energy source when glucose is unavailable.
Components of the Lac Operon
1. Structural Genes:
lacZ: Encodes β-galactosidase, which breaks lactose into glucose and galactose.
lacY: Encodes lactose permease, which transports lactose into the cell.
lacA: Encodes thiogalactoside transacetylase, with a lesser-known function in lactose metabolism.
2. Regulatory Regions:
Promoter (P): Binding site for RNA polymerase to initiate transcription.
Operator (O): Binding site for the lac repressor protein that blocks transcription.
Regulatory Gene (lacI): Produces the lac repressor, which inhibits the lac operon when lactose is absent.
Regulation of the Lac Operon
1. In the absence of lactose:
The lac repressor (produced by lacI) binds to the operator, blocking RNA polymerase.
This prevents transcription of the lacZ, lacY, and lacA genes, conserving energy.
2. In the presence of lactose:
Lactose (or its isomer, allolactose) binds to the lac repressor, causing it to change shape and detach from the operator.
RNA polymerase can now transcribe the structural genes, allowing lactose metabolism.
#lacoperon#generegulation#class12#biology

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