Q5 of 44 Page 79

A plasmid DNA and a linear DNA (both are of the same size) have one site for a restriction endonuclease. When cut and separated on agarose gel electrophoresis, plasmid shows one DNA band while linear DNA shows two fragments. Explain.

•When endonuclease makes cut on the specific restriction site of the circular DNA of plasmid, the circular DNA changes into linear DNA.


•But, when endonuclease makes cut within the linear DNA it would result in formation of two linear DNA fragments.


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3

A recombinant DNA molecule was created by ligating a gene to a plasmid vector. By mistake, an exonuclease was added to the tube containing the recombinant DNA. How does this affect the next step in the experiment i.e. bacterial transformation?

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Restriction enzymes that are used in the construction of recombinant DNA are endonucleases which cut the DNA at ‘specific-recognition sequence’. What would be the disadvantage if they do not cut the DNA at specific-recognition sequence?

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How does one visualise DNA on an agarose gel?

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A plasmid without a selectable marker was chosen as vector for cloning a gene. How does this affect the experiment?