Question

2. p-Nitrophenyl galactoside is a colorless compound that is hydrolyzed by β-galactosidase to yield galactose and p-nitrophenol, which is intensely yellow. Why is this compound not used for screening colonies for the presence or absence of active β-galactosidase? (5 points).

3. Use curved arrows to show the chemical mechanism for DNA ligation by DNA ligase in the presence of ATP. You only need to show the reaction on one strand and this part of the report can be written by hand. (10 points).

Answer 1

2)

Pera-Nitrophenyl galactoside is a colorimetric and spectrophotometric substrate.

It is also using for the detection of β-galactosidase activity.

It is normally colorless but if β-galactosidase is present, it hydrolyzes the Pera-Nitrophenyl galactoside molecule into galactose and pera-nitrophenol.

yellow color of the compound can be used to check for enzyme activity and further it is required to check the utilization of lactose so we can measure the enzymatic rate.

But whenver it is used for screening colonies to determine the presence or absence of active β-galactosidase, This stage unable to act as an inducer for the lac operon and Without another lactose analog that will not act as an inducer so this compound not used for screening colonies for the presence or absence of active β-galactosidase.

3)

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