MCAT Question of the Day
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    Q:

    		 Recombinant plasmids are used to clone gene fragments encoding desired proteins. They are constructed by cutting the plasmid vector (containing an ampicillin resistance gene) and gene insertion fragments with restriction enzymes such that the end fragments of the cut sites match with each other. The cut plasmid vector and insertion fragment are then ligated together with the enzyme ligase to form the recombinant plasmid. This recombinant plasmid can be transformed into competent bacteria and plated onto agar plates with ampicillin, where only bacterial colonies with the recombinant plasmids can grow. Colonies can then be picked and have their recombinant plasmids amplified via PCR (polymerase chain reaction).

    In which the following experimental conditions will we not expect bacteria colonies to grow on agar plates with ampicillin?

    		 

    A

    		 Competent bacteria mixed with a plasmid vector which has been cut with two different restriction enzymes (resulting in nonidentical cut sites), and reacted with ligase.

    B

    		 Competent bacteria mixed with uncut plasmid vector.

    C

    		 Competent bacteria mixed with cut plasmid vector and insertion fragment with ligase.

    D

    		 Competent bacteria mixed with plasmid vector cut with a single restriction enzyme and reacted with ligase.



    Recombinant DNA and Biotechnology | Prokaryotes |
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