Question

I just recently conducted an experiment in my biochemistry class where we had to add DNA to distilled water, isotonic saline and 2.5M NaCl. I noticed different physical aspects depending on the solvent, but I'm not sure how I would categorize them. Here's what I saw:

• Distilled: fibrous precipitate, cloudy liquid

• Isotonic: Honestly barely noticed a change here? Maybe I wasn't looking hard enough

• 2.5M: salt precipitate at the bottom and fibres

I know DNA is polar so solubility should increase as the polarity of the solvent increases. But to my recollection what I saw in 2.5M saline vs distilled water did not differ much. However, there is always the possibility that I could have made some experimental errors that led to inaccurate observations.

Answer 1

You likely salted out your DNA at your high concentration of salt. The salt preferentially interacted with the solvent and itself that would have held the DNA in solution.