If we ligate a foreign DNA at the BamHI site in pBR322, then the recombinant plasmid will:
A. Show tetracycline resistance
B. Grow on tetracycline containing medium
C. Show ampicillin resistance
D. Not grow on ampicillin containing medium
Answer (1)
To answer the question about the effect of foreign DNA insertion at the BamHI site in the pBR322 plasmid, we need to understand a bit more about the plasmid’s structure and its role in antibiotic resistance.
pBR322 is a commonly used plasmid vector in genetic engineering that carries two antibiotic resistance genes: one for ampicillin resistance (Amp^R) and another for tetracycline resistance (Tet^R). These genes allow researchers to select for bacteria that have taken up the plasmid by growing them on mediums containing these antibiotics.
The plasmid has multiple restriction sites where foreign DNA can be inserted. When foreign DNA is inserted at the BamHI restriction site, it occurs within the tetracycline resistance gene. This disruption generally inactivates the Tet^R gene, thus causing loss of tetracycline resistance in the recombinant plasmid.
Given this background, the likely outcomes are:
Show tetracycline resistance: The recombinant plasmid will NOT show tetracycline resistance because the insertion of foreign DNA at the BamHI site disrupts the Tet^R gene.
Grow on tetracycline containing medium: Due to the inactivation of the Tet^R gene, bacteria containing the recombinant plasmid will NOT grow on a tetracycline-containing medium.
Show ampicillin resistance: The Amp^R gene is unaffected by the insertion at the BamHI site, so the recombinant plasmid will continue to confer ampicillin resistance.
Not grow on ampicillin containing medium: This statement is incorrect because the Amp^R gene remains intact, allowing growth on an ampicillin-containing medium.
Based on this understanding, the correct concepts related to the insertion of foreign DNA at the BamHI site are:
The recombinant plasmid will show ampicillin resistance.
It will not grow on a medium containing tetracycline.
This is a typical strategy used in molecular biology for selecting bacteria containing recombinant plasmids, by relying on selective markers like antibiotic resistance genes.
