Final answer:
Peptide groups are rigid and planar because of the double bond character of the peptide bond, which results in no free rotation. This rigidity affects the orientation of the peptide backbone and facilitates hydrogen bonding between the N-H and C=O groups. It also allows peptides to fold into complex tertiary structures.
Step-by-step explanation:
The peptide bond has a double bond character, which gives it rigidity. This is due to resonance, which results in about 40% double bond character in the bond. As a result, there is no free rotation around the peptide bond. The four groups around the peptide bond exist in the same plane, similar to alkenes.
The rigidity of the peptide bond affects the orientation of the peptide backbone, limiting its possible orientations. The N-H groups in the peptide bond can form hydrogen bonds with the C=O groups within the same chain or between neighboring chains. These hydrogen bonds play a crucial role in determining the secondary and tertiary structures of proteins.
Peptides, which are composed of peptide bonds, can fold into complex tertiary structures. The rigidity and planarity of the peptide bond contribute to the ability of peptides to adopt specific conformations and play important roles in biological processes.