Lac Operon

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  • Topic: Lac operon, Gene expression, Operon
  • Pages : 3 (1124 words )
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  • Published : April 25, 2007
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Short Report: Lac Operon.
The lac operon is a set of structural genes that consists of one regulatory gene, Lac I, and three structural genes: Lac Z, Lac Y and Lac A [1,2]. Lac I codes for the repressor protein of the lac operon. Lac Z codes for b-galactosidase, which hydrolyze lactose into glucose and galatose [1,2]. Lac Y codes for permease, which increases permeability of the cell to b-galactosides [1,2]. Lac A codes for transacetylase, which detoxifies certain byproducts of lactose metabolism [1,2]. In addition, there is a Promoter region, the binding site for RNA polymerase, and an Operator region, the binding site for repressor protein. In the present of lactose, it binds to the repressor protein and induces a conformational change that prevents the repressor protein from binding to the Operator. As a result, RNA polymerase is able to proceed, and encodes Lac Z, Lac Y and Lac A into β-galactosidase, permease, and transacetylase, respectively, Figure 1 [3]. Consequently, lactose is metabolized. On the other hand, in the absence of lactose and in the present of glucose, the repressor protein that is coded from Lac I is in its original conformation and able to bind to the Operator. This inhibits RNA polymerase from carry out its function because RNA polymerase cannot proceed past the Operator. As a result, there is no RNA is made and by extension, no enzyme is made, Figure 2 [3].

Figure 1: Lac operon in the present of lactose. [3]

Figure 2: Lac operon in the absent of lactose. [3]
The purposes of this lab were to observe different phenotypes and how the bacteria are behaving in different types of media. Four different genotypes of bacteria were used: I+P+Z+, I+P-Z+, I-P+Z+, and I+P+Z-. Genotype I+P+Z+ is the wild type, in which everything gene is normal. Genotype I+P-Z+ has mutated gene P, which do not allow promoter to bind very well; therefore, the level of β-galactosidase is very low. Genotype I-P+Z+ has mutated gene I, which make the...
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