DNA has a negative charge due to phosphate groups, and therefore it is often ass

Question

DNA has a negative charge due to phosphate groups, and therefore it is often associated with positive sodium ions (Na^+). If the DNA-sodium complex is introduced into water, which of the following would be expected? A1. The dielectric constant of the water would decrease due to the added DNA and sodium. A2. The positive charges of two sodium ions would repel each other more strongly. A3. The water would efficiently hydrate the DNA but not the much smaller sodium ions. A4. The water would strengthen the association between sodium ions and DNA. A5. None of the above would be expected.

Explanation / Answer

If the DNA-sodium complex is introduced into water, the water would stregthen the association between sodium ions and DNA. This is because each phosphodiester bond in DNA is negatively charged , this negative chage protects the bond from spontaneous hydrolysis by water. As the halflife of the bond is increased, the association between sodium ions and DNA is strengthened.

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