As explained in the PDB summary page and Chapter information, the ribose unit at the has flipped outwards, and uracil has been .

Hydrogen has only one electron in its only (and outer) electron shell. if a hydrogen atom were to absorb a small amount of energy, where would bohr say the electron would go? a. fly off the atom b. nowhere, it would just speed up. c. spiral inwards towards the nucleus d. move up to another shell that would form