Final answer:
The 3D structure of a peptide backbone is made up of peptide bonds that allow for limited movement due to their partial double bond character, influencing secondary and tertiary structures through hydrogen bonding and interactions among R groups.
Step-by-step explanation:
The bonds that exist in the 3D structure of a peptide backbone are primarily composed of peptide bonds between amino acids. These bonds exhibit about 40% double bond character due to resonance, which restricts free rotation around the bond, keeping the connected groups in the same plane.
This characteristic influences the secondary and tertiary structures of the peptide chain. The secondary structure features hydrogen bonding between the N-H groups and the C=O groups, forming patterns such as the α-helix and β-pleated sheets.
The tertiary structure involves more complex interactions, including hydrogen bonds as well as ionic bonds and other interactions among the R groups of the amino acids, contributing to the three-dimensional arrangement of the polypeptide
.