Peptide Backbone (View 2) (Pepides)

A fragment of polypeptide backbone is shown above without the actual side chains. Note the following general features of peptide units:
Label the atoms in residue 2.
Highlight the four atoms in the second peptide unit as Ball & Stick.
Color black, the peptide bond.
Rotation, with preferred dihedral angles, occurs around these two backbone bonds:
  (Psi), rotation about the CA2-C2 single bond; and
  (Phi), rotation about the N2-CA2 single bond.

Some facts on Peptide bonds.
The atom-labelling used above are RasMol abbreviations:

The peptide bond (C2-N3, and colored black above) joins amino acids in the primary structure of polypeptides. The partial double bond character of the peptide bond keeps the peptide unit rigidly planar. The oxygen of each peptide unit is nearly always trans to the amide hydrogen. The peptide bond is sometimes designated as "omega".
Adjust the model so that both peptide units lie in a plane from your perspective, and note that there is only one way to do so. Similarly, if the PHI and PSI angles in a polypeptide are specified, its backbone conformation is completely defined.

Return to image of peptide bonds.