Structure of Protein

Primary structure: Each protein has a unique sequence. Primary structure is like a finger print, each one has a unique structure. Peptide bond (hydrogen bonds)

Secondary structure: Random coil structure (beta casein, due to high amount of beta proline); Alpha helix structure (the more frecuent, the residues are oriented towards the exterior part of the helix); beta sheet structure (More stable).

Tertiary structure: protein folds again and forms a 3d structure, due to the action of the interactions

Quaternary structure: Oligomeric structure, polypeptide chain, combined proteins. Due to all  different interactions we can create the complex structure of the protein.