1)Show in the figure below are the melting curves for two DNA samples that were

Question

1)Show in the figure below are the melting curves for two DNA samples that were thermally denatured under the same conditions.

A) What conclusion can you draw concerning the base composition of the two samples? Explain

B) How might explain the steeper slope of the melting curve for sample A?

C) Formamide and urea are agents known to form hydrogen bonds with pyrimidines and purines. What effect, if any, would the inclusion of a small amount of formamide and urea in the incubation mixture have on the melting curves?

Explanation / Answer

A. Sample A has higher GC content compared to sample B. Sample A melts at higher temperatures than sample B. It indicates it has more GC content since the three bonds between the bases GC require more energy to break the bonds.

B. The steepness of the curve in sample A indicates that the distribution of G+C occurs at a narrow range. The other curve is not as steep as sample A which means that it has the distribution of bases more uniform across the given range of melting curve.

C. Formamide and urea interact with the bases and disrupt their hydrogen bonding properties. Therefore, addition of urea and formamide destabilize the DNA by forming hydrogen bonds, as a result of which the DNA melts at still lower temperatures.

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