Nuclei have been isolated from a stem cell line at 0, 1, 2, and 4 days after the
ID: 214947 • Letter: N
Question
Nuclei have been isolated from a stem cell line at 0, 1, 2, and 4 days after the cell line has been induced to differentiate into muscle type cells. The nuclei are subjected to digestion with DNase, the DNA is then extracted from the nuclei and cleaved with a restriction enzyme that cleaves the DNA external to genes X and Y. The digestion products are run on a gel and analyzed by Southern blots using a labeled probe that binds to either X or Y DNA (or RNA). The results of this experiment are shown on the Southern blot below at the left. The experiment is repeated, but without DNase, and the results are shown on the Southern blot below in the middle. Finally, RNA, extracted from the cells at days 0, 1, 2 and 4 after induction, is run on gels which are then blotted and probed for the presence of X or Y RNA, as shown in the Northern blot below, right.
a. Why do the patterns of bands differ between the two Southern blots?
Days of induction01 2 4 0 1 24 Probe X Probe Y | Southern blot Southern blot Northern blotExplanation / Answer
Why do the patterns of bands differ between the two Southern blots?
when southern boot us carried out, there is production of a break in the DNA. There would be the use of restriction enzyme, which in this case is the DNase. After the fragments would be run on the gel, there would be use of specific labelled sequences, which in this case are X or Y. While in the gel, the sequences of DNA get separated as a result of their length. The one having the shortest sequence would travel far and the sequence that is the longest, would travel the least. As a result, the patterns observed are as a result of location of the restriction site or the number of the restriction site in which the DNA is cut. If there is removal of a restriction site or addition of a restriction site, there would be shifting of the target site on another band on the gel.
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