Question

Primary structure of protein is due to
A. Hydrogen bonds
B. Peptide bonds
C. $-S-S-$ linkages
D. Ionic bonds

Answer 1

Hint: The primary structure of proteins refers to the sequence of amino acids that are joined with one another by forming a bond between the carboxyl groups of one amino acid with the amino group of another amino acid which is a type of covalent linkage.

Complete answer:
Option (A) is incorrect. H-bonds are not present in the primary structure of a protein. These bonds are present in the secondary structure of a protein. The secondary structure of protein includes alpha-helix and beta-pleated sheets which are held in shape by H-bonds.
Option (B) is correct. The primary structure of a protein is simply the sequence of amino acids in a polypeptide chain. The carboxyl group of one amino acid is connected with the amino group of another amino acid, leading to the formation of a peptide ($-CONH$) bond.
Option (C) is incorrect. Disulfide linkages are present in the tertiary structure of a protein. These linkages are covalent linkages between the sulfur-containing side chains of cysteine residues. These bonds are known for keeping parts of the polypeptide chain firmly attached.
Option (D) is incorrect. Ionic bonds are present in the tertiary and quaternary structures of the protein and are known for stabilizing these structures of the protein.

Hence, the correct answer is option (B).

Note: Proteins are present all over in the body and the structure of a protein is due to different amino acids. Different amino acids are joined together in a linear sequence by peptide linkages or$-CONH$linkages only. The formation of a peptide bond is an example of a condensation or elimination reaction in which one molecule of water during the formation of a peptide bond between two amino acids.