Let's suppose you followed the protocols described in...

Let's suppose you followed the protocols described in Figures 20.2 and $20.3 .$ Which experiment(s) would you conduct to confirm that a white colony really contained a recombinant vector with an inserted fragment of DNA? a. Pick a bacterial colony and restreak on plates containing $\mathrm{X}$ -Gal to confirm that the cells really form white colonies. b. Pick a bacterial colony, isolate plasmid DNA, digest the plasmid DNA with a restriction enzyme, and then perform gel electrophoresis with the DNA. c. Pick a bacterial colony and test it to see if $\beta$ -galactosidase is functional within the bacterial cells. d. Pick a bacterial colony and retest it on ampicillin-containing plates to double-check that the cells are really ampicillin resistant. e. Both c and d should be conducted.

Let's suppose you followed the protocols described in Figures 20.2 and $20.3 .$ Which experiment(s) would you conduct to confirm that a white colony really contained a recombinant vector with an inserted fragment
of DNA?
a. Pick a bacterial colony and restreak on plates containing $\mathrm{X}$ -Gal to
confirm that the cells really form white colonies.
b. Pick a bacterial colony, isolate plasmid DNA, digest the plasmid DNA with a restriction enzyme, and then perform gel electrophoresis with the DNA.
c. Pick a bacterial colony and test it to see if $\beta$ -galactosidase is functional within the bacterial cells.
d. Pick a bacterial colony and retest it on ampicillin-containing plates to double-check that the cells are really ampicillin resistant.
e. Both c and d should be conducted.

Key Concepts

Recombinant DNA Cloning

This concept involves inserting a fragment of foreign DNA into a vector so that the resulting recombinant molecule can be introduced into a host cell and propagated. It underlies many molecular biology techniques, allowing researchers to manipulate genes, study gene function, or produce proteins by using the host's replication machinery.

Blue-White Screening

Blue-white screening is a molecular technique used to distinguish between bacterial colonies that contain a recombinant vector and those that do not. It relies on the disruption of the lacZ gene, which normally produces a blue pigment in the presence of X-gal. Colonies with an intact lacZ gene turn blue, while those with an insertion (and therefore disrupted lacZ) remain white.

Plasmid Isolation

Plasmid isolation is the process of extracting plasmid DNA from bacterial cells. This step is critical for downstream analyses such as restriction enzyme digestion, sequencing, or further cloning studies. Successful isolation ensures that clean DNA is available for confirming the presence of the inserted DNA fragment.

Restriction Enzyme Analysis

Restriction enzyme analysis involves using specific enzymes that cut DNA at defined sequences. By digesting the isolated plasmid with these enzymes, and then analyzing the resulting DNA fragments, one can confirm the presence and correct size of an inserted DNA fragment in the vector.

Gel Electrophoresis

Gel electrophoresis is a laboratory method used to separate DNA fragments based on their size and charge. After restriction enzyme digestion, running the fragments through a gel allows researchers to visualize and confirm the size of the DNA fragment inserted into the vector, providing evidence of successful cloning.

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