Figure 1:

This is a molecular model of the 3-fold channel with the three (3) intersecting subunits represented as ribbons. (In this picture, the ribbons have the same color code as the ribbons in Figure 1 in the main section of this tutorial.) The amino-acid residues lining the channel are shown as CPK models. Notice the polarity of the carboxylate sidechains on the residues lining the 3-fold channel; the polar nature of these sidechains results in this channel being hydrophilic.

Note: The carbon atoms are green, the nitrogen atoms are blue, and the oxygen atoms are red in the CPK model.