4) You are given two samples of DNA, each of which melts at 92oC during thermal

Question

4) You are given two samples of DNA, each of which melts at 92oC during thermal denaturation. After denaturing the DNA, you mix the two samples together then cool the mixture to allow the DNA strands to reassociate. When the newly reassociated DNA is denatured a second time, the sample now melts at 85oC.

A) How might you explain the lowering of the melting temperature from 92oC to 85oC?

B) What kind of experiment could be carried out to test your hypothesis?

C) If the newly reassociated DNA had melted at 92oC instead of 85oC, what conclusions might you have drawn concerning the two initial DNA samples?

Explanation / Answer

A. Strands might be similar but not identical. There might be regions of similar nucleotide sequences. Strands of one sample might hybridize with strands of the other DNA, which is not identical. The resulting hybrids will have regions of non-complementarity, where base pairing did not occur, and hence, result in a decrease in melting point.

B. Base sequencing can be done to test the hypothesis. If the hypothesis is true, both the DNA have similar sequences, but not identical

C. The two initial samples must have identical DNA sequences is this case. Therefore, there is complete complementarity, and thus, no change in the melting temperature.

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