ring agarose gel electrophoresis of DNA, shorter DNA molecules typically migrate

Question

ring 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 Band B DNA is negatively supercoiled, whereas band A DNA is O O Q o positively supercoiled Band B DNA is less supercoiled than band A DNA. Band B DNA is more supercoiled than band A DNA. Relaxed DNA is more susceptible to DNA damage, resulting in two populations of DNA size groups. Topoisomerase I supercoiled band B DNA and topoisomerase lI supercoiled band A DNA

Explanation / 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 (option 5)

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