For the following restriction endonucleases, calculate the average distance betw

Question

For the following restriction endonucleases, calculate the average distance between restriction sites in an organism with a random DNA sequence and equal proportions of all four nucleotides. The symbol R means any purin (A or G), Y means any pyrimidine (T or C), and N stands for any nucleotide. Show your work.

a. RsaI 5GTAC3. _________________________________________________

b. SauI 5CCTNAGG3. _____________________________________________

c. CviJI 5RGCY3. _________________________________________________

2. You are attempting to determine if the new DNA sample you have just received contains linear or circular molecules. Digestion using either RsaI or SauI alone produces two fragments. On the basis of the results for the single digests, how many fragments would you expect for the RsaI/SauI double digest if the DNA is linear? How many fragments would you expect if the DNA is circular? Justify your answers.

Explanation / Answer

The probability = (The probability of each of the nucleotide pairs, i.e. (1/4)) * (probability of specified pairs i.e.(1/2) for R-Y and 1 for N)). As the distance is expressed interms of base pairs, reciprocal of the probability is taken for calculations.

Rsal, 5GTAC3 = (4)(4)(4)(4) = 256 base pairs distance

Saul, 5CCTNAGG3 = 46 = 4096 base pairs distance

CviJI, 5RGCY3 =  (4)(4)(2)(2) = 64 pairs distance

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