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

Explanation / Answer

1. If the DNA is more supercoiled (positively or negatively), then it moves faster. Let us analyse the option based on this fact.

Option a) Band B DNA is more supercoiled than band A DNA. This is correct.

Option b) The type of topoisomerase enzyme does not influence the degree of supercoiling. This is incorrect.

Option c) According to the fact, this is also incorrect.

Option d) More supercoiled DNA moves faster. So this is also incorrect.

Option e) The band separation is due to supercoiling. So this is also incorrect.

ANSWER: Band B DNA is more supercoiled than band A DNA.

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