I asked a question on this post,

In a Chromosome, 2 nm is the length of what?

about a part of this figure.

enter image description here

the whole thing is a Chromosome, and I would like to know what the first part is, so, is "2 nm is the length of what" a clear and idiomatic question?

  • 1
    You can rephrase the question as “in a chromosome, what is 2 nm long?” In general, this type of question may have more than one correct answer. Commented Jul 31, 2019 at 13:20

1 Answer 1


It is quite clear to me what your question is. If the DNA structure is a helix, then you can call that dimension its diameter.

This Wikipedia page contains the sentence

This value may be directly measured using an atomic force microscope to directly image DNA molecules of various lengths. In an aqueous solution, the average persistence length is 46–50 nm or 140–150 base pairs (the diameter of DNA is 2 nm), although can vary significantly.

Here is another reference

The diameter of the helix is 20 Å.

Since 1 Ångstrom = 0.1 nanometre that is consistent with your diagram.

So you can say

In a chromosome, 2 nm is the length of the diameter of the DNA.


In a chromosome, the diameter of the DNA is 2 nm.

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