Figure 3.

Two of the twenty different kinds of amino acids in the modeling kit are shown. (a) Proline is an atypical amino acid with an extra bond that connects back to the amino group. It is one of many hydrophobic (yellow) amino acids. (b) Glutamic acid, a typical hydrophilic amino acid with a long side pink chain. The colors of the side chain indicate the four chemical groups: hydrophobic amino acids are yellow (no charge), the hydrophilic amino acids are blue (positive charge), pink (negative charge), and green (polar with negative and positive charges). The chemical diagrams illustrate how the side chains (-R groups) were stylized in the models to indicate relative differences in size and shape. © MIT Edgerton Center Protein Booklet 1.