Page "Protein" Paragraph 7

Most proteins consist of linear polymers built from series of up to 20 different-α-amino acids.

All proteinogenic amino acids possess common structural features, including an α-carbon to which an amino group, a carboxyl group, and a variable side chain are bonded.

Only proline differs from this basic structure as it contains an unusual ring to the N-end amine group, which forces the CO – NH amide moiety into a fixed conformation.

The side chains of the standard amino acids, detailed in the list of standard amino acids, have a great variety of chemical structures and properties ; it is the combined effect of all of the amino acid side chains in a protein that ultimately determines its three-dimensional structure and its chemical reactivity.