"Size" of a DNA molecule? Sorry for such a beginner's question in an advanced profile forum: In basic school we were taught that a molecule of a substance is "the smallest structure which still retains all the properties of that substance. If you divide it any further, (at least some of) its properties are gone". Based on this very simplistic interpretation, is it possible (or meaningful) to define "the minimum size of a DNA molecule"? My guess is "no", and if that's right, where is the point where the above simplistic definition of "a molecule" breaks down?, and what should be the proper definition of "a molecule" for complex substances with very variable sizes such as DNA? Thanks!