Question

1. If a restriction enzyme cuts a circular plasmid twice, how many fragments would you see on the gel?

2. How would you estimate the total number of base pairs in a plasmid by looking at the DNA fragments of the digested plasmid on a gel?

3. If a linear 1kb DNA fragment has a restriction site that is located 50 bp from one end of the plasmid, what would you expect to see if the digested and undigested DNA samples were run on a 1% agarose TAE gel?

Answer 1

1)

If a restriction enzyme cut a plasmid two times,then two fragments are obtained.

Look in the image for diagrammaric representation:

2)

We also load a DNA ladder in the well of gel electrophoresis. We also load our digested sample in the gel. Then look for the corresponding band fragments. And compare it with the DNA ladder. In this way, the molecular weight of fragments are obtained.

3) There is found one restriction site in the plasmid. That's why the digested plasmid have linear DNA.

The uncut plasmid have two forms open circular DNA and supercoiled DNA. The following pattern is observed in the gel.

Supercoiled DNA runs faster than open curcular DNA because of less friction.

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