Proteins exhibit two secondary structures, a-helix, and b-pleated sheet, resulting from hydrogen bonding between >C=O and –NH– groups in the peptide bond. The a-helix forms a right-handed screw, while the b-pleated sheet resembles pleated folds of drapery.

The primary structure of proteins refers to the specific sequence of amino acids in a polypeptide chain. Any alteration in this sequence creates a distinct protein, making the primary structure crucial for protein identity.