The command ribbon shows a ribbon representation of the secondary structure of proteins and nucleic acids; ~ribbon turns off the ribbon display. The ribbon does not replace any atoms, but is added to the current display. Protein secondary structure is determined from HELIX and SHEET records in the input file, or if these are not present, using ksdssp. For nucleic acids, the ribbon simply follows the phosphodiester backbone. No ribbon is drawn for molecules that are not proteins/peptides or nucleic acids.
The type of ribbon shown can be changed with the command ribrepr, the Actions menu, or the molecule model attributes panel.
Even if only particular atoms are specified, the ribbon segment(s) corresponding to the entire residue(s) containing the atoms will be affected.
The color of the ribbon is assigned on a per-residue basis (for example, using ribcolor or rainbow) and may differ from the apparent color of the residue's atoms; see coloring hierarchy. If ribbon colors have not been assigned, the ribbon defaults to the model-level color.
See also: ribrepr, rainbow, ribcolor, modelcolor, the Actions menu, the Ribbon Style Editor tool