Question

33.       Referring the plasmid in question 31, to test for the presence of this plasmid in a strain of E. coli, what antibiotic should be added to the media?

31.. You are carrying out a restriction endonuclease digestion. You wish to add 0.5 unit enzyme to the reaction. The specific activity of the enzyme is 10 U/ul how much enzyme should you pipet out?

Answer 1

Solution 31.

The calculation is a case of cross-multiplication.

Number of units per ul (microliter) = 10
Required number of units = 0.5

Let the required volume be 'X' uL.

Now,

X = (0.5) / (10)

X = 0.05uL

Therefore, to obtain a specific activity of 0.5 units, one should add 0.05 microliters of the enzyme.

Solution 33

"Insufficient information, since Q.31 does not mention any plasmid"

However, generally either penicillin or streptomycin is added to the media to screen for recombinants. The plasmids usually contain antibiotic resistance genes for penicillin and streptomycin.