Comment by dekhn
20 hours ago
It's not really just base pairs forcing groove structure. The repulsion of the highly charged phosphates, the specific chemical nature of the dihedral bonds making up the backbone and sugar/base bond, the propensity of the sugar to pucker, the pi-pi stacking of adjacent pairs, salt concentration, and water hydration all contribute.
My graduate thesis was basically simulating RNA and DNA duplexes in boxes of water for long periods of time (if you can call 10 nanoseconds "long") and RNA could get stuck for very long periods of time in the "wrong" (IE, not what we see in reality) conformation, due to phosphate/ 2' sugar hydroxyl interactions.
Jeffhwang is correct, and dekhn is thinking way too hard. If you have any asymmetric planar structure that stacks into a helix into the third dimension there will be a minor groove and a major groove.