Question

You have a piece of circular DNA that can be cut by the restriction nucleases XhoI and SmaI, as indicated in Figure Q10-5.

If you were to cut this circular piece of DNA with both XhoI and SmaI, how many fragments of DNA would you end up with?
(a) 1
(b) 2
(c) 3
(d) 4

Answer 1

The correct answer is option b. Assuming each restriction enzyme (XhoI and SmaI) has one recognition site on the circular DNA molecule, digestion with both would typically result in two linear DNA fragments. Without specific information about the number of recognition sites, the answer is based on a general understanding of restriction digestion.

Step-by-step explanation:

The subject of this question is related to restriction endonucleases, enzymes that cut DNA at specific recognition sites. The student is asked about the number of fragments that would result from cutting a circular piece of DNA with two restriction enzymes: XhoI and SmaI. This pertains to the branch of biology known as molecular biology or genetics. The outcome of such a digestion depends on the number of recognition sites for each enzyme on the DNA molecule. If there is one recognition site for each enzyme, cutting with both enzymes will result in two fragments.

However, if there are multiple sites for one or both enzymes, the number of resulting fragments will be higher. Since the question does not provide the number of recognition sites or a figure, a general understanding of restriction digestion and plasmids are used to answer the question.

If we assume that each restriction enzyme (XhoI and SmaI) has one recognition site on the circular DNA molecule, digestion with both enzymes would result in two linear fragments. Therefore, the answer would be (b) 2. However, if the exact number of sites for each enzyme is unknown, one cannot say with certainty without additional information or the specified figure.