Concept explainers
To analyze:
The inducibility of a gene that is mediated by activator and repressor in response to change in environmental conditions, with the help of suitable diagram.
Introduction:
An operon is a stretch of DNA which consists of a cluster of functionally related genes. It contains an operator, promoter, and related genes. It is present only in prokaryotes. It was first characterized in E. coli. Operon can be inducible or repressible.
Inducible operon: In presence of substrate, transcription of structural gene occurs, and in
absence of substrate, the operator region is occupied by the repressor so, RNA polymerase is unable to bind at promoter region, and transcription cannot be initiated. In inducible operon, transcription in inhibited in absence of the substrate.
Repressible operon: In repressible operon, the substrate acts as a co-repressor that facilitates the conformational change in the repressor of the operon and transcription is inhibited in absence of co-repressor. The conformation of original repressor does not allow it to bind to the operator region of the operon. Thus, the operator region is free and RNA polymerase can bind at the promoter region, and transcription of genes can be initiated.
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