Proteins have up to four levels of organic structure.
1.Primary structure - the linear arrangement of amino acids.
2. Secondary structure - areas of folding or coiling within a protein.
3. Tertiary structure - the final three dimensional structure of a protein.
4. Quaternary structure - non covalent associations that bind multiple polypeptides into a single larger protein. E.g. hemoglobin has four polymers, two alpha and two beta chains. They are non covalently bound to each other to form a single large protein - hemoglobin.