The specific spatial structure of proteins determines their diverse physiological functions. 1.Structure. Primary structure, the order of amino acids from the N-terminus to the C-terminus. Secondary structure, the localized spatial structure of a segment of the peptide chain in a protein molecule. Tertiary structure, the relative spatial position of all amino acid residues in the whole peptide chain. Tertiary structure, the spatial arrangement of the subunits of a protein molecule and the layout and interaction of the subunit contact sites. 2. Functions: composition of cell and organism structure, material transportation, catalytic function, information exchange, immune function, oxidative function, maintenance of acid-base balance, maintenance of normal plasma osmotic pressure.