- * Planar peptide bonds
- Resonance constrains the peptide bond, so that it CANNOT rotate, which gives the polypeptide sequences a backbone with little room for conformational change.
- Almost all peptide bonds are in trans configuration.
Peptide Bond Essentials
We show a peptide bond between two amino acids in 3D with one R-group coming towards you and one R-group facing away from you.
Planar peptide bonds
The peptide bonds linking amino acids are planar, meaning that both alpha carbons and the atoms of the peptide bond lie in the same plane.
Resonance
- Resonance is the term that we apply to the fact that the double bond within the peptide bond can shift between carbon-oxygen to carbon-nitrogen.
- Resonance constrains the peptide bond, so that it CANNOT rotate, which gives the polypeptide sequences a backbone with little room for conformational change.
The two possible configurations for the peptide bond are:
- trans – in which the oxygen and hydrogen atoms face two different directions.
- cis – in which the oxygen and hydrogen atoms face the same directions.
Almost all peptide bonds are in trans configuration.
- We draw large circles around the R groups of the cis to help us visualize why peptide bonds favor this configuration. R’s are not just small letters but represent large groups of atoms (like in the side chains of tryptophan and histidine) that can interact with or interfere with each other if they get too close.