The protein tube is a spline curve that passes through all the C atoms in a protein fragment. Five evenly spaced interpolation points are found along the curve to break the curve connecting the two C atoms into six line segments. If the first C is selected, the first three segments are colored by the color assigned to that C. If the second C is selected, the last three segments are colored by the color of the second C. The nucleic acid tube is constructed in the same manner except that the phosphate atoms are used.
The two controls set the spline radius and resolution and have the same meaning as they did in the `Bond' control. However, if the bond's Radius becomes 0 or Resolution is 2 or less then the spline is drawn as a simple line. This make moving and rotation the image much faster.
It is possible to pick with the mouse the C which defines the tube by clicking near the middle of the six tube segments which are associated with that atom.