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.

Protein structure can be studied at four levels: primary, secondary, tertiary, and quaternary. Each level represents increasing complexity, with primary being the simplest and quaternary being the most complex.

Globular proteins have a spherical shape formed as polypeptide chains coil around. They are generally soluble in water. Examples of globular proteins include insulin and albumins.

Fibrous proteins have a fiber-like structure with parallel polypeptide chains held together by hydrogen and disulphide bonds. Examples include keratin (in hair, wool, silk) and myosin (in muscles).