The Secondary Structure of a protein refers to the folding or coiling of the polypeptide chain into specific patterns like the $\alpha$-helix or $\beta$-pleated sheet.

• These structures are primarily stabilized by Hydrogen Bonding between the carbonyl oxygen ($-C=O$) of one peptide bond and the amide hydrogen ($-NH-$) of another peptide bond in the backbone.
• Peptide bonds stabilize the primary structure (sequence).