Lac Operon

602 Words3 Pages
The lactose (lac operon) is a group of genes used by bacterial cells as an energy saving mechanism to regulate the expression of the structural genes which are needed to metabolise lactose, one of the main energy sources for a bacterial cell when glucose is not readily available. The lac operon consists of a region of DNA, a promoter for a regulatory gene, a regulatory gene (lacI), a promoter, an operator and the three structural genes; lacZ, lacY and lacA. The function of the promoter for the regulatory gene is to encode for the regulatory gene (lacI) which is the main regulator of the operon. The protein formed by the lacI gene known as the lac repressor regulates the turning on and off of the operon in response to lactose concentration by…show more content…
Another molecule is necessary for the regulation of the lac operon, this is a protein called cyclic AMP receptor protein (CRP) which is required as the lac promoter is a weak promoter. This protein binds to the promoter region and initiates the binding of RNA polymerase which begins transcription. The three structural genes are essential for the metabolism of lactose into glucose and galactose, the lacZ gene codes for the enzyme β-galactosidase which breaks down lactose, the lacY gene encodes for β-galactosidase permease which brings lactose into the cell and the function of the lacA gene, transacetylase is unknown. When lactose is not available, the lacI gene is bound to the promoter, when lactose becomes available the low levels of β-galactosidase convert lactose to allolactose which is the inducer of the lac operon. The binding of allolactose to lacI causes the lacI to leave the promoter and prevents it from binding to the operator allowing the initiation of transcription. The regulation of gene expression is extremely important as it conserves energy for the cell by turning off genes when they are not necessary and it prevents the overproduction of different proteins which could potentially lead to abnormalities in the…show more content…
The regulation of gene expression could be examined effectively as both strains were grown in different media and they both possessed different genotypes. The wild type strain was grown overnight in 1 x A media supplemented with thiamine and the mutated strain was grown in 1 x A media, supplemented with thiamine in the presence of the compound isopropylthiogalactoside (IPTG). IPTG is a synthetic inducer of the lac operon. Allolactose is the usual inducer of the lac operon but it is very unstable and hard to use in the laboratory, IPTG is a favourable
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