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Question 2 (12 points)

A purified DNA preparation of a certain plasmid is

digested to completion with BamH1 restriction endonuclease. In separate reactions, the same preparation was digested to completion with EcoRI and with a mixture of EcoRI and BamH1, respectively. The diagram below shows the appearance of the original molecules and the digestion products in the three digestion mixtures, after separation by electrophoresis in an agarose gel. (Note: Uncut supercoiled circular DNA migrates further in a gel because it is more compact in size than a linear DNA fragment of the same sequence length. The distance a supercoiled DNA molecule migrates on a gel is not an accurate indication of its sequence length.)

Lane M--Linear DNA Markers of the indicated length in kb

Lane 1--Sample of the original plasmid DNA preparation

Lane 2--Sample of the products of BamH1 digestion

Lane 3--Sample of the products of EcoRI digestion

Lane 4--Sample of the products of digestion of BamH1 + EcoRI

Answer and justify the following:

a. What was the original DNA molecule's length?

6 Kb

b. Was the original plasmid DNA circular or linear?


c. How many restriction sites for EcoRI and BamH1 did the original plasmid have?

d. Draw the original plasmid, using B and E to indicate the location of the BamH1 and the EcoRI restriction sites. Indicate the number of kb between sites.

Top Answer

a.) 6 Kb (kilobyte) b.) circular c.) There are 2 restriction sites for the EcoRI and 1... View the full answer

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