Protein has four levels of structure in total, of which the tertiary structure has to be extended by step by step, through the primary structure to the secondary to tertiary structure. Primary structure of protein: refers to the order of amino acid arrangement in the polypeptide chain, called primary structure, and the main chemical bond is peptide bond. Secondary structure: refers to the local spatial structure of a section of the peptide chain in the protein molecule, the relative spatial position of the backbone atoms of the main chain of the peptide chain, and does not involve amino acid residues, the conformation of the side chain, the secondary structure bond is hydrogen bond. Tertiary structure: refers to the relative spatial position of all amino acid residues in the whole peptide chain, called protein tertiary structure, mainly ionic bonds, hydrogen bonds, etc.