Ampicillin is broad-spectrum antibiotic that prevents the growth of bacteria tha

Question

Ampicillin is broad-spectrum antibiotic that prevents the growth of bacteria that are lacking the plasmid. X-Gal is a substrate for a reaction that is catalyzed by beta-galactosidase, which is encoded by the lacZ gene.

Ampicillin is broad-spectrum antibiotic that prevents the growth of bacteria that are lacking the plasmid. X-Gal is a substrate for a reaction that is catalyzed by beta-galactosidase, which is encoded by the lacZ gene. Suppose a scientist wants to clone the gene for human insulin. He uses a plasmid that contains the IacZ gene, an origin of replication, and an ampicillin resistant gene. He inserts the human insulin gene into a restriction site located within the IacZ gene. Then he transforms this plasmid into bacteria without a functional lacZ gene and spread the appropriate dilution onto bacterial plates. When the product of the IacZ gene, beta-galactosidase, interacts with the subtrate X-Gal on LB agar, colonies turn blue. Which of the plates below indicates the human insulin gene was successfully inserted in the plasmid? an LB agar plate with ampicillin and X-Gal that produces blue colonies an LB agar plate with ampicillin that produces colorless colonies an LB agar plate with ampicillin and X-Gal that produces colorless colonies an LB agar plate with ampicillin that produces blue colonies

Explanation / Answer

For transformation of human insulin gene to bacteria, plasmid containing the gene of interest (insulin gene), lac Z gene encoding beta- galactosidase, ampicillin resistance gene and origin of replication is constructed and cloned into bacterium. The genes, lac Z and ampicillin resistant gene are much useful in the screening of transfomed bacteria in a suitable medium. For example, if the medium contains he X - gal substrate then the cells containing the lac Z gene express beta - galactosidase gene and produce blue colored colonies to identify the transormed cells easily. Likewise the cells containing ampicillin resistance gene do not grow in medium containing ampicillin.

Thus in the above given example, an LB agar plate with ampicillin and X - Gal that produces colorless colonies is correct. This is becaue the cells resistant to ampicillin and that do not contain lac Z gene are grown and these are nontransformed cells. Option 3 is correct.

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