Chemistry
Why Peptide Bonds Are Planar and How That Constrains Protein Folding
Quick fact
The peptide bond is planar because its constituent atoms, along with the alpha carbons, lie in a flat plane due to resonance. This planarity prevents free rotation around the C-N bond, leaving only two adjacent bonds free to rotate, giving rise to the phi and psi dihedral angles that determine protein backbone conformation.
Why this is interesting
You might think that the parts of a protein chain can twist and rotate freely, but there is a stubborn lock in every peptide bond that rigidly flattens it. What causes this lock, and how does it limit the shapes a protein can take?