The default ribbon path is a smooth bspline (semitransparent tan in the figure), which can diverge from the true positions of the backbone atoms (α-carbons shown as gray balls). A cardinal spline allows tracking the backbone more closely. Without smoothing (light blue), it follows the α-carbons exactly, or it can be combined with some “compromise” smoothing of strand and/or coil. Ribbon spline options can be set with the ribspline command or in the molecule model attributes.

Large ribosomal RNA is shown with individual bases depicted using solvent excluded molecular surfaces. Bases A, C, G, U are colored red, yellow, green, and blue. The surfaces were made with the Chimera multiscale tool in combination with the nucleic acid blobs plug-in. The image was raytraced using POVray.

Protein Data Bank model 1s72.