thumb|right|200px|An α-helix in ultrahigh-resolution electron density contours, with oxygen atoms in red, nitrogen atoms in blue, and hydrogen bonds as green dotted lines (PDB file 2NRL, 17–32). The N-terminus is at the top, here.
thumb|right|200px|An α-helix in ultrah.igh-resolution electron ,density contours, with oxygen atoms in red nitrogen atoms in blue, and hydrogen bonds as green dotted lines (PDB file 2NRL, 17–32). The N-terminus is at the top, here