Structure of Protein

Primary: Sequence of amino acids linked by peptide bonds (positional info); Secondary: Local folding (right-handed alpha-helix, beta-pleated sheets) stabilized by H-bonds; Tertiary: 3D folding forming 'active sites' for enzymes (stabilized by disulfide/ionic bonds); Quaternary: Assembly of multiple polypeptide subunits (e.g., adult Hemoglobin has 2 alpha, 2 beta chains).