Question

Two double helix DNA molecules of equal length are melted. The first dissociates at a lower temperature than the second. What would this indicate about the relative contents of nucleotides in the two molecules?

a. it tells only that they differ in nucleotide makeup, nothing more.
b. the first molecule has a higher content of C-G base pairs than the second molecule.
c. the second molecule has a higher content of C-G base pairs than the first molecule.
d. the first molecule has nucleotides that are spaced closer together, therefore it has more nucleotides than the second molecule. the second molecule has nucleotides that are spaced closer together, therefore it has more nucleotides than the first molecule.

Answer 1

The DNA molecule that dissociates at a higher temperature has a higher content of C-G base pairs, which are more stable due to three hydrogen bonds compared to the two hydrogen bonds in A-T base pairs.

Step-by-step explanation:

If two double helix DNA molecules of equal length are melted and the first dissociates at a lower temperature than the second, this indicates that the second molecule has a higher content of C-G base pairs. The correct answer is c. the second molecule has a higher content of C-G base pairs than the first molecule. This conclusion is based on the fact that C-G base pairs form three hydrogen bonds compared to the two hydrogen bonds of A-T base pairs. Therefore, more energy (higher temperature) is required to break these additional hydrogen bonds, making DNA with a higher GC content more stable and less prone to denaturation at lower temperatures.

Learn more about DNA Melting and Base Pair Content