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*Explain how the presence of glucose represses the gal structural genes.

*Explain how the presence of glucose represses the gal structural genes.

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The gal operon is a prokaryotic operon and is responsible for encoding enzymes important for galactose metabolism. The operon is regulated by binding of two repressor molecules leading to gene expression. The gal operon in E.coli consists of three structural genes which are galE, galT and galK. When the system detects high concentration of glucose, tetrameric GalR repressor binds to 2 operators, one at +55 and one that is located at +60. This leads to formation of open complex as it causes blocking of access of RNA polymerase to the promoters and inhibits formation of the open complex. It is the glucose based catabolite repression that leads to the induction of the galactose metabolic genes or GAL genes.

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