tertiary structure

The three-dimensional structure of a protein or nucleic acid. Amino acids form secondary structures such as alpha helices, beta sheets, and random coils, which in turn fold on themselves to form the tertiary structure of the protein. Only if a protein is correctly folded will it have its intended biological activity. Several diseases, such as cystic fibrosis and mad cow disease, are caused by alterations in the tertiary structure of one or more proteins. See also primary structure quaternary structure secondary structure.