In the recent Nature Chemistry paper I-motif DNA structures are formed in the nuclei of human cells (open access link in LATimes) figure 1a shows "Schematic of i-motif and G4 structures."

Schematic of I-motif and G4 structures

I'm not a biologist, nor a chemist, so please forgive if the answer to my questions seems obvious. I've looked at Wikipedia's Structural Motif article but there's little there about nucleic acids.

  1. The length of the unlinked strand seems shorter, is this just because it is a schematic, and in reality the two branches would have the same number of bases?
  2. What does the presence of the dual left and right arrows in G4$\ce{<-->}$ iM in the figure mean in this case? Does it suggest that a single molecule can change configuration back and forth between two distinct structures, or something else?

closed as off-topic by David, WYSIWYG Apr 24 '18 at 8:05

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  • $\begingroup$ Double arrows represent reversible reactions. Your question is not really about biology but about the correctness of a schematic. Therefore I shall put this question on hold. BTW, both your guesses are right. $\endgroup$ – WYSIWYG Apr 24 '18 at 8:05
  • $\begingroup$ @WYSIWYG thanks for your comment. I'm trying to understand how all those bonds can re-arrange between those two configurations, and if this is actually known to happen. My intended question is to explore how DNA can do this but I wanted to check first if I was interpreting the diagram correctly or not, perhaps I was being overly methodical. If I rewrote to make this clearer, asking if DNA can do this, how, and if it is known to do this (move between these two configurations) would that be potentially on-topic? $\endgroup$ – uhoh Apr 24 '18 at 8:12
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    $\begingroup$ Yes, if you edit your question such that it is about how DNA attains a certain configuration then your question is on topic. However, make sure that you are not asking a broad question. $\endgroup$ – WYSIWYG Apr 24 '18 at 8:14
  • $\begingroup$ @WYSIWYG thanks for your help, I'll take a day or so and try to do some additional reading. $\endgroup$ – uhoh Apr 24 '18 at 8:24
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    $\begingroup$ When you edit the question ping me in the comment or vote to reopen. Ideally, the question should show up in the reopen review queue if it is edited post closure. $\endgroup$ – WYSIWYG Apr 24 '18 at 8:27

To answer point 1: The length of the unlinked strand is not represented accurately, it is shown shorter only because this is a schematic. In reality, the unlinked strand should be the same length, and would have the same number of bases as you have guessed.


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