Please answer # 1,2,3,4,and 5 Repression of the lac operon by the repressor prot

Question

Please answer # 1,2,3,4,and 5

Repression of the lac operon by the repressor protein is an excellent example of a negative control mechanism (the expression of a gene is turned off by the binding of the repressor protein). The lac operon is also under positive regulation (the expression of a gene is turned on by the binding of a protein). The following are a series of statements and questions describing the positive control of the lac operon. The procedure for completion of this portion of the exercise is the same as for the first exercise. As stated earlier, glucose is the preferred energy source in bacterial cells. Even if glucose and lac- Toes are both present in the growth medium, the glucose will be used first and the lactose utilization genes will not be transcribed until the glucose has been depleted. The levels of glucose within a bacterium are correlated with and communicated by the levels of cAMP. cAMP (cyclic AMP) is a derivative of ATP which is studied in greater detail in other lectures. WHEN GLUCOSE LEVELS ARE HIGH, cAMP LEVELS ARE LOW. WHEN GLUCOSE LEVELS ARE LOW, cAMP LEVELS ARE HIGH. The third control site in the lac operon is a binding site for the catabolite activator protein (CAP). The binding site for CAP (c) in the lac operon is immediately adjacent to the promoter (-72 to -52). Do you think it is possible for the CAP and RNA polymerase to be bound to the control region of the lac operon simultaneously? Do you think it possible for the CAP and lac repressor to be bound simultaneously? cAMP binds to CAP, which is (you guessed it) an allosteric protein. The CAP-cAMP complex has a higher affinity for its binding site than CAP alone. in addition, the presence of CAP-cAMP complex at the regulatory region greatly increases the affinity of RNA polymerase for the promoter site. Under what nutritional circumstances (high or low glucose) is CAP bound to cAMP? Would you hypothesize that the binding of the CAP-cAMP complex to the lac operon control region increases or decreases transcription from the operon? in the absence of lactose and the presence of glucose in the bacterial growth media, what proteins are bound to the lac control region? Is the operon being transcribed? in the presence of lactose and the presence of glucose in the bacterial growth media, what proteins are bound to the lac regulatory region? Is the operon being transcribed? in the presence of lactose and the absence of glucose in the bacterial growth media, what proteins are bound to the lac control region? Make modifications to the diagram (see Figure 1) to illustrate the regulation of lac by cAMP and CAP. Complete the table provided, indicating how much (lots, little, none) of the lac z gene product would be made given the following mutations: mutation in the operator that reduces the affinity of the operator for the repressor protein (operator-constitutive mutants = o^c)?

Explanation / Answer

1.As cAMP bound CAP facilitates the binding og RNA polymerase to the promoter, DNA binding site while the initiation of transcription, it is possible.Yes.

2.During the availabilty of glucose the cAMP is low and as it decreases cAMP forms a complex with CAP.Increases.

3.Lactose repressor binds to the lac operator site preventing the binding of RNA polymerase to the Beta-galactosidase,permease,and transactylase and as a result they are not transcribed.

4.Presence of both glucose and lactose tuns off transcription because CAP cannot bind.

5.In the absence of glucose, catabolite repressor is tuned off; RNA polymerase binds to the promoter and transcribes Beta-galactosidase,permease,and transactylase genes.

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