During agarose gel electrophoresis of DNA, shorter DNA molecules typically migra

Question

During agarose gel electrophoresis of DNA, shorter DNA molecules typically migrate faster than longer molecules. When closed-circular DNA molecules of the same size possess different linking numbers, these DNA molecules will also separate during agarose gel electrophoresis. A sample of purified plasmid DNA of uniform length was separated on an agarose gel and stained, as shown below. In addition to a strongly stained band (B), the gel shows a faintly stained band (A) that migrated a much shorter distance. Select the statement that explains why two bands appeared in the migration pattern O Band B DNA is less supercoiled than band A DNA Topoisomerase l supercoiled band B DNA and topoisomerase ll supercoiled band A DNA. Relaxed DNA is more susceptible to DNA damage, resulting in two populations of DNA size groups. Band B DNA is more supercoiled than band A DNA. Band B DNA is negatively supercoiled, whereas band A DNA is O positively supercoiled How would the addition of DNA ligase and DNA gyrase to the plasmid sample prior to electrophoresis alter the migration pattern'? The linking number of the DNA will increase.

Explanation / Answer

1. apart from the crucial size, the mobility of DNA is also very important.in case of plasmid, the supercoiled DNA moves faster and goes at the base whereas the relaxed circular DNA travelled very short distance. thus,

band B DNA is more supercoiled than band A DNA as B has moved faster than A

2. DNA gyrase is a type of topoisomerase. it is used to unwind the double-helical structure of DNA. it opens the DNA.

DNA ligase helps in the joining of the DNA.

when gyrase and ligase is added to the plasmid, this will change the linking number of the DNA. thus,

the linking number of DNA will increase

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