Which of the following structures represents the peptide chain?

A peptide bond, also referred to as an amide bond, is formed between the $\boldsymbol{\alpha}$-nitrogen atom of one amino acid and the carbonyl carbon of a second amino acid.
Related Theory Long chain polypeptides can be formed by linking many amino acids to each other via peptide bonds. The peptide bonds of proteins are metastable, and will break spontaneously in a slow process.