The lac operon - Below: Allolactose, an isomer of lactose,...

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The lac operon Lactose is a sugar found in milk. If lactose is present, E. coli (the common intestinal bacterium) needs to produce the necessary enzymes to digest it. Three different enzymes are needed. In the diagrams below, genes A, B, and C represent the genes whose products are necessary to digest lactose. In the normal condition, the genes do not function because a repressor protein is active and bound to the DNA preventing transcription. When the repressor protein is bound to the DNA, RNA polymerase cannot bind to the DNA. The protein must be removed before the genes can be transcribed.
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Unformatted text preview: Below: Allolactose, an isomer of lactose, binds with the repressor protein inactivating it. The repressor protein is produced by a regulator gene . The region of DNA where the repressor protein binds is the operator site. The promoter site is a region of DNA where RNA polymerase can bind. The entire unit (promoter, operator, and genes) is an operon . The operator acts like a switch that can turn several genes on or off at the same time. The lac operon is an example of an inducible operon because the structural genes are normally inactive. They are activated when lactose is present....
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The lac operon - Below: Allolactose, an isomer of lactose,...

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