Note that in DNA crystal structures, hydrogens (H) are not detected (why?) and so are not shown in the structure at right. Compare the structure above with that at right.

Consequently, chemists and biologists who look at these structures have to figure out where the hydrogens are placed based on their knowledge of chemistry.

Knowledge of where the H's are is important in assessing the hydrogen bonding characteristic of a base pair. Note that some of the nitrogens have lone pairs (again you have to use your knowledge of chemistry to assess where the lone pairs are placed).

Hilight a N that has a lone pair.
Hilight O's that have lone pairs.