Hi all!

 

I'm having trouble visualizing a question that asks to compare double-stranded DNA in a solution of PH 7 with a low salt concentration or in water with no ions. In which solution would DNA have a lower melting temperature?

 

I know that DNA is a polar molecule that is negatively charged. Would the ions in the first solution neutralize the DNA and allow it to more easily dissociate (lower melting temperature) than the DNA in the water that wouldn't neutralize the molecule? Or does it have to do more with which one allows it to more easily hydrogen bond?

The charge of DNA is primarily due to the phosphate groups in the sugar backbone. But first for the definitions. What does melting of DNA mean (or using your words, what should dissociate?). And what is the bond that holds it together?

Dear Goosegirl,

 

As you said DNA is a negatively charged molecule and presence of salt should stabilize the DNA molecule. If you think in stability and energy categories it meands that when there are positively ions present in the solution DNA should be more stable than in the solution which lack those interactions. So in my opinion DNA will have lower melting temperature in the water (less ions) because is less stable what means that you need to provide less energy from outside to denature it. I hope that is true and it helps:)

 

GGSTEAM

 

http://www.bio-ggs.blogspot.com