Question

An investigator carefully isolates plasmid DNA with an alkaline lysis method, which is designed to minimize damage to the plasmid structure. The plasmid contains 4300 bp of DNA. What should the investigator expect to see on an agarose gel?

Answer 1

Answer:

On the agarose gel, primarily four different forms of plasmid DNA is observed which are explained below.

Explanation:

• Alkaline Lysis Method is the commonly used biochemical technique for isolating plasmid DNA from bacterial cells.
• When the isolated plasmid DNA is subjected to electrophoresis on an agarose gel and observed after ethidium bromide staining, it is seen to get separated into four distinct bands sequentially from bottom to top,

1. Circular and single-stranded form which migrates fastest among all.
2. Supercoiled form which migrates after the circular form.
3. Linear form which migrates after the supercoiled form.
4. Nicked circular form which migrates last.

• The variation in intensity of the bands determines which form of the plasmids is mostly present in the isolated sample.
• If minimal damage is done to the plasmids, the band of supercoiled form  of the plasmid will glow with maximum intensity.