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Name: Sally
Status: Other
Grade:  Other
Location: N/A
Country: United States
Date: February 2008

Why do not DNA bases form hydrogen bonds with cellular water?

Bases are able to hydrogen bond water, but they'd rather bond with each other. This is because the base-base bond in DNA is "thermodynamically favored" (which basically means that all molecules are lazy, and it takes more work for the bases to bond with water than it does to bond with water). The structure of DNA also helps -- the DNA coils around itself, and the backbone of DNA shields the bases somewhat from water. There are enzymes that 'unzip' the DNA, and while the DNA is unzipped, it can bind with sites on the enzyme or with other water molecules. Overall, DNA that's zipped tends to stay zipped.

That's true at living temperatures. The answer changes when you heat up DNA. If you boil the water the DNA is in, the DNA will uncoil and the bases will bond with water instead of other bases. This is known as 'denaturing' -- it's a very useful fact that is used in PCR (polymerase chain reaction) -- look it up!

Hope this helps,

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