Question : 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.

Question : A plasmid DNA and a linear DNA (both are of the same size)

1.	Question : 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.
Answer» Solution : It is because plasmid is a circular DNA molecule. When cut with enzyme, it becomes linear but does not get FRAGMENTED. Whereas, a linear DNA molecule gets cut into TWO FRAGMENTS. Hence, a single DNA band is OBSERVED for plasmid while two DNA BANDS are observed for linear DNA in agarose gel.