E. coli cells are growing in a medium containing lactose but no glucose. Indicate whether each...

E. coli cells are growing in a medium containing lactose but no glucose. Indicate whether each of the following changes or conditions would increase, decrease, or not change the expression of the lac operon. For full credit, you must explain your answer. It may be helpful to draw a model depicting what is happening in each situation.

(a) Addition of a high concentration of glucose

(b) A mutation that prevents dissociation of the Lac repressor from the operator

(c) A mutation that completely inactivates ?-galactosidase

(d) A mutation that completely inactivates galactoside permease

(e) A mutation that prevents binding of CRP to its binding site near the lac promoter

Expert Solution

(a) Addition of a high concentration of glucose
The main carbon source of bacteria is glucose. In the absence of glucose, the bacteria will depend on other carbon sources. If the glucose is present in the media, it shifts in to glucose, it leads to decrease of the gene expression.

(b) A mutation that prevents dissociation of the Lac repressor from the operator
The RNA polymease can move over the operator, but here repressor totally binds to operator, so it inhibits the RNA polymease action by blocking its way, so, it leads to decrease of the gene expression.

(c) A mutation that completely inactivates ?-galactosidase
?-galactosidase acts only on lactose, the inactiavte b galactosidase wont cause any effect on gene expression.

(d) A mutation that completely inactivates galactoside permease
Galactoside permease increases the permeability of lactose in the cell. A muation which inactivates it, it blocks the entrance of lactose in to cell which leads to decrease of the gene expression.

(e) A mutation that prevents binding of CRP to its binding site near the lac promoter
In the absence of glucose, CRP enhaces the expression of lac operon. Here this mutation, leads to decrease of the gene expression.

gladiator answered 1 year ago

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