There are two ways to draw a `Tube' representation,
one for proteins and the other for
nucleic acids. The protein tube is a smooth curve through the
selected C positions, and the nucleic acid tube is a smooth curve through the backbone phosphates.
The protein tube is a spline curve that passes through all the
Cs in a protein fragment. Five evenly spaced interpolation
points are found along the curve to break the curve connecting the two
C
s 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 the `Bond' control. However, if the bond radius becomes 0 or the bond 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.