: Not all polymers are built up from bonding together a single kind of repeating unit.At the other extreme,protein molecules are polyamides in which n amino acid trpeat units are bonded together.Although we might still call n the degree of polymerization in this case,it is less useful,since an amino acid unit might be any one of some 20-odd molecules that are found in proteins.In this case the molecular weight itself,rather than the degree of polymerization,is generally used to describe the molecule. When the actual content of individual amino acids is known,it is their sequence that is of special interest to biochemists and molecular biologists.