Submit reasoning and process, not merely answers! Problem Set 4: DNA Structure a

Question

Submit reasoning and process, not merely answers!

Problem Set 4: DNA Structure and Replication Submit reasoning and process, not merely answers! 1. You work at the Center for Disease Control and have been given to analyze a suspected bioterror agent that may be a type of Variola, a double-stranded DNA virus that is the causative agent of smallpox. Smallpox was one of humanities major scourges, killing as many as 500 million people in the 20h century. It is believed to have been wiped out in 1979 with arn aggressive vaccination campaign. Since few alive today are resistant to smallpox, a live virus could wreak havoc To analyze the virus, you obtain DNA from the precious sample of purified virus and (asa control) from canine parvovirus, a single-stranded DNA virus you happen to have on hand Unfortunately, you forget to label the two tubes! What else to do but to continue. so you analyze the two DNA samples for nucleotide composition (in the same way as Chargaff) giving the results shown below. Which tube contains which Variola DNA, and why? Recovery 93.2 94.1 Tube 1 15.7 33.4 32.7 11.4 Tube 2 18.7 34.4 26.9

Explanation / Answer

To find ds DNA or ss DNA , the following composition is considered. A/T ratio = 1 ; G/C = 1 for ds DNA For ss DNA A/T = 0.77 and G/ C = 1.3 . Here if we perform the calculation , both the DNAs in tube A and B get more or less similar values Tube A , A/T = 1.02 ; G/c =1.3 Tube B , A/T = 1.2 ; G/C = 1.3 But in tube A, T/A = 1 and in tube B T/A = 0.77. Thus, Tube A must contain double stranded DNA . This is because the ratio of A/ T = 1.02 and the ratio of T/ A = 1 . This is possible only if it is double stranded DNA. In Tube B , the ratio of A/T = 1.2 which is higher than 1 and the ratio of T/ A is 0.75 . These values shows that A and T composition is not equal . Hence tube B must be ssDNA.

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