Question

A DH5-alpha E. coli with an insert in the lacZ-alpha locus is spread on various media containing X-gal. Choose which of the following apply to these bacteria.

Select one or more:

a. They will produce a functional alpha-acceptor

b. They will not grow on ampicillin and produce blue colonies on non-ampicillin medium

c. They will grow on ampicillin and produce white colonies

d. They will not grow on ampicillin and produce white colonies on non-ampicillin medium

e. They will produce a functional alpha-donor

f. They will grow on ampicillin and produce blue colonies

g. They will not produce a functional alpha-acceptor

h. They will not produce a functional alpha-donor

Answer 1

Option C, they will grow on ampicillin and produce white colonies.

Explanation

Functional beta galactosidase enzyme is made up of two subunits- alpha and beta subunit

DH5 alpha E coli contains beta subunit of beta galactosidase enzyme.

While alpha subunit is produced by plasmid containg lacZ alpha gene plunder LacZ promoter.

In this plasmid if insert DNA is absent- than intact LacZ alpha gene- produce alpha subunit and produce functional betagalactocidase in EColi . This enzyme act on X gal convert it in to blue colour product and colonies appears blue coloured.

If insert DNA is present in MCS ( multiple cloning site), it disrupts lac Z alpha gene- no alpha gene - no functional beta galactosidase gene- X gal us not converted in to blue coloured products and colony appears to white.

One more thing only those Ecoli cell will grow has plasmid , as we are growing cells I'm ampicillin medium. E ci do not have ampicillin resistant gene . So only EColi cell has plasmid ( it carry ampicillin resistant gene) will grow.

E coli with plasmid-- grow on ampicillin medium

E coli with intact plasmid-- blue colour colonies due to presence of intact lac Z alpha protein

E coli with plasmid with foreign gene-- white colonies