damn. i'm guessin this class is killin you eh? not quiet clear on the question there...u need to be more accurate, this answer can go many ways with just that kind of wording.
but...2 structures of DNA...
1: the Bases of DNA (ACTG) these are hydrogen bonded to the opposite bases on the opposite strand of DNA, this together makes the double helix
2: the sugar/phosphate backbone....this is the backbone of the DNA
but...2 structures of DNA...
1: the Bases of DNA (ACTG) these are hydrogen bonded to the opposite bases on the opposite strand of DNA, this together makes the double helix
2: the sugar/phosphate backbone....this is the backbone of the DNA
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http://en.wikipedia.org/wiki/DNA