Comprehension

We know that plasmids and bacteriophages are the most commonly used vectors in biotechnology experiments. If we can link an alien piece of DNA to the plasmid DNA, the alien DNA can be multiplied equal to the copy number of the plasmid. Engineered vectors are used these days. Study the diagram of the E. coli cloning vector pBR322 and answer the questions that follow :

Question: 1

Why are plasmids and bacteriophages used as cloning vectors ?

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A high "copy number" means that multiple identical copies of the vector exist within a single host cell, which directly increases the yield of the cloned target gene.

Updated On: Aug 16, 2026

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Question: 2

Identify (I) the specific gene in the standard pBR322 cloning vector that controls the copy number, and (II) the specific restriction site located within the 'rop' gene sequence.

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- ori: Controls replication and plasmid copy number. - rop: Codes for the repressor of primer protein, which regulates replication. It contains the target restriction site PvuII.

Updated On: Aug 16, 2026

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Question: 3

Identify and name the two selectable markers present in the structural diagram of the E. coli cloning vector pBR322.

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Selectable markers are essential for identifying recombinants. Without them, it is difficult to isolate the few cells that successfully took up the modified plasmid from the many that did not.

Updated On: Aug 16, 2026

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Question: 4

Name the two distinct restriction enzyme recognition sites located within each of the two selectable marker genes ($amp^R$ and $tet^R$) of plasmid pBR322.

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Inserting a foreign gene at the BamHI or SalI site inactivates the tetracycline resistance gene. This means recombinant bacteria will lose their resistance to tetracycline but remain resistant to ampicillin.

Updated On: Aug 16, 2026

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