Bacteria and other microbes can be used to \"clean up\" an oil spill by breaking

Question

Bacteria and other microbes can be used to "clean up" an oil spill by breaking down oil into carbon dioxide and water. Two samples isolated from the Deepwater Horizon leak in the Gulf of Mexico were labeled A and B. The DNA of each was isolated and the percent thymine measured in each sample. Assume the organisms contain normal double-stranded DNA and predict the composition of the other bases. Both samples are then denatured to remove the secondary structure. Which will have the higher temperature to denature?

Explanation / Answer

Ans. Ans. Using Chargaff’s rule for dsDNA-        

            No. of A nucleotides = No. of T nucleotides, -----equation 1

            No. of G nucleotides = No. of C nucleotides, ----- equation 2

Sample A: Given, A = 17.3 %

Thus, T = 17.3 %      [Using equation 1]

Now,

G + C = 2 G [G = C, equation 2]

Or, 2C = 100 – (A+ T) = 100 – (2 x 17.3 %) = 100 % - 34.6 % = 65.4 %

Or, C = (65.4) / 2 = 32.7 %

Hence, C = G = 32.7 %

Sample B: Given, T = 29.5 %

Thus, A = 29.5 %      [Using equation 1]

Now,

G + C = 2 G [G = C, equation 2]

Or, 2C = 100 – (A+ T) = 100 – (2 x 29.5 %) = 100 % - 59 % = 41 %

Or, C = (41 %) / 2 = 20.5 %

Hence, C = G = 20.5 %

#2. A DNA with higher GC content has higher melting temperature because GC pair forms 3 H-bonds per pairs when compared to 2 H-bonds per AT pair.

Thus, sample A has higher melting temperature because its GC content (65.4%) us higher than that of sample B (41 %).

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