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Wikipedia, for example, refers to DNA as "a" molecule, not two separate molecules forming a double-helix structure. Isn't this technically incorrect? There are two separate polynucleotide strands (each that can be considered one molecule on its own as the monomers are joined together by covalent bonds), and the strands joined together by hydrogen bonds and not covalent/ionic bonds along their length. Doesn't that exempt them from being considered one molecule, as the bonds joining them are intermolecular and not covalent or ionic?

Bill Wilson
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  • If we considered a double-helix to be two separate molecules, then how do describe two separate double-helices? I think using the singular "molecule" with a double helix is appropriate because it makes it easy to use the plural "molecules" when referring to a group of DNA double-helices. Also, there are other supramolecular complexes such as Catenanes and Rotaxanes which are generally referred to as singular molecules despite having no covalent bonds between the parts. – user137 Jun 06 '19 at 08:28
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    DNA is a molecule. dsDNA is a supramolecular structure. Wikipedia is not the authority on biochemical nomenclature. You can edit Wikipedia to correct this. – WYSIWYG Jun 06 '19 at 08:28
  • I'm voting to close this question as off-topic because it is about the correctness of a wikipedia article. The question may also become invalid if wikipedia is corrected. – WYSIWYG Jun 06 '19 at 08:32
  • Also, it is a possible duplicate of https://biology.stackexchange.com/q/66343/3340 – WYSIWYG Jun 06 '19 at 08:43
  • Wikipedia was just an example. The answers to the question linked seem to say that DNA is one molecule. The text referenced in Charles' answer (Molecular Biology of the Cell) says one, single DNA molecule is 2 polynucleotide chains, just like Wikipedia. I find the answer abut DNA being a polyatomic ion/2 polyatomic ions to be the most accurate, since a molecule is by definition uncharged (or only partially charged). – Bill Wilson Jun 07 '19 at 12:50
  • @BillWilson — I look forward to your next publication in which you refer repeatedly to DNA as a complex of two polyatomic ions. The ion thing is irrelevant anyway (it is always balanced by cations) and you have essentially the same problem with haemoglobin. How are you going to refer to that? I think you need to emerge from your chemist’s cocoon and think about the state of science when, and the purpose for which, the term “molecule” was devised. Compare that with the state and purpose today, and the practicality of using words to communicate ideas. – David Jun 07 '19 at 14:15
  • @Bill Wilson The word "molecule" is usually meant to describe a "thing" on the atomic scale. Even the IUPAC definition essentially says a molecule is an "entity" bigger than 1 atom (note the lack of bond types). https://goldbook.iupac.org/html/M/M04002.html. The reason why dsDNA is called a molecule is likely because the two strands behave as one entity in physiological contexts. – user40950 Jun 07 '19 at 16:46
  • For all intents an purposes dsDNA "entities" will behave as a single molecule when handled in the lab unless you heat them above melting temperature or add chemicals and reactants that modify the strands. – Jeppe Nielsen Jun 25 '19 at 17:27

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