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. O Band B DNA is more supercoiled than band A DNA. Band B DNA is negatively supercoiled, whereas band A DNA is positively supercoiled Topoisomerase I supercoiled band B DNA and topoisomerase II supercoiled band A DNA. Relaxed DNA is more susceptible to DNA damage, resulting in two populations of DNA size groups. Incorrect. The two bands shown in the migration pattern do not result from damage to the DNA sample. How does supercoiling affect DNA migration through an agarose gel? How would the addition of DNA ligase and DNA gyrase to the plasmid sample prior to electrophoresis alter the migration pattern? Band B will disappear.

Explanation / Answer

Answer:

Band B is more supercoiled than band A as band B has traveled much more further and faster than band B.

Gyrase negatively supercoils the plasmid DNA which will change the linking number differently in different plasmid molecules giving a series of different bands

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