The bond type responsible for maintaining the primary structure of proteins is:

The bond type that maintains the primary structure of proteins is the peptide bond. Peptide bonds form between the amino group of one amino acid and the carboxyl group of another, creating a covalent bond that links amino acids together in a linear chain. The sequence of amino acids in this chain defines the primary structure of a protein, which is fundamental to its overall function and properties.

While other bond types are important for the higher-order structures of proteins—such as hydrogen bonds stabilizing secondary structures like alpha-helices and beta-sheets, and disulfide bonds providing stability in tertiary and quaternary structures—these bonds do not affect the primary structure itself. The primary structure solely relies on the specific order and the covalent nature of peptide bonds to maintain its integrity. Thus, peptide bonds are essential for establishing the basic framework of proteins.