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I've read that the primary obstacle to the compaction of chromatin is the negative charge on the DNA phosphate-sugar backbone. This negative charge is slightly stabilized by the positive charges on histone proteins. In solutions with high salt concentrations, chromatin adopts a more condensed state, whereas in solutions of low salt concentration, chromatin is less condensed. The explanation I found was that cations from the salt help provide additional stabilization to the negative charges on the DNA molecules—thus, solutions with higher cation concentration promote greater condensation of chromatin.

But what about the anions in the solution? A solution must be electrically neutral; when salt concentration increases, the concentrations of both cations and anions increase. Even if the salt cations stabilize the DNA's negative charge, won't this be perfectly offset by electrostatic repulsions between the DNA and the salt anions?

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I think the 'whereas' part is excessive and misleading - I'd say "Higher concentration results to more condensed state". So charge of DNA + solution will be the same but it will be distributed differently:

$$ D^{-} + nK^{+} + nA^{-} \rightarrow (D^{-}+mK^{+}) + (n-m)K^{+} +nA^{-} $$

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  • $\begingroup$ Could you explain what the symbols in your formula mean? $\endgroup$ – lightweaver Feb 25 '17 at 3:12
  • $\begingroup$ D - DNA, K - cation, A - anion, n - number of water molecules, m - number of attached to DNA cations. $\endgroup$ – Maxim Kuleshov Apr 3 '17 at 15:04

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