Describe what you understand by the primary structure and secondary structure of proteins.

Primary structure of proteins: Each polypeptide chain in a protein has amino acids linked with each other in a specific sequence. This sequence of amino acids is said to be the primary structure of proteins.

2. The secondary structure of proteins: The secondary structure of proteins refers to the shape in which a long polypeptide can exist. The two different secondary structures possible are α-helix structure and β-pleated sheet structure.

(i) α-Helical structure: In α-Helix structure, a polypeptide chain forms all possible hydrogen bonds by twisting into a helix with -NH group of each amino acid residue and hydrogen bonded to >C=O of an adjacent turn of the helix. The structure can be drawn as follows.

(ii) β-pleated structure: In a β-pleated structure, all peptide chains are stretched out to nearly maximum extensions and then laid side by side which are held together by intermolecular hydrogen bonds.