DNA Structure and Replication

ID #1718

Why is this statement false: "Melting temperature is defined as the temperature at which 50% of a population of dsDNA molecules are in a fully single stranded form."

There is a fundamental difference between saying "the point at which a given molecule of DNA is 50% denatured" and saying "the point at which 50% of a population of molecules are fully denatured." Provided all the molecules in your population were identical in sequence (which they would have to be to determine Tm in the first place), why would one molecule be expected to behave differently than a molecule identical to it? It wouldn't. Instead, each of the molecules will begin to denature at essentially the same point, and they will all collectively reach a point at which they are all half unwound. Whatever temperature you're at when you reach this point is the melting temperature of that particular sequence of DNA.

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