Figure 1
A short protein chain of 3 amino acids is shown for the purpose of illustrating protein geometry. All amino acids share a common set of atoms, N (in blue), C α (in gray), C (in gray), and O (in red), known as the backbone atoms. The set of atoms that makes an amino acid unique and confers to it a specific type is known as the side chain. Side chains for the shown chain are encapsulated in the violet spheres labeled S 1 through S 3. There are 20 different types of naturally-occurring amino acids. Side chains dangle off the backbone chain that connects the backbone atoms of consecutive amino acids. There are two backbone dihedral angles, φ and ψ, per amino acid. These angles are annotated over the shown backbone chain.