Enzymes are biological catalysts: biopolymers that catalyze a reaction. Although a small number of natural enzymes are built from RNA–termed Ribozymes–most enzymes are proteins. Like any other protein, an enzyme is an amino acid polymer with added cofactors and other post-translational modifications. Often, most of the amino acid polymer is indirectly involved with the enzymes function, perhaps providing ancillary structure or connectivity, indirect activity regulation, or molecular identification of the enzyme. As a result, most enzymes are large molecules weighing many kilodaltons. This bulk can obscure various investigative techniques such as NMR, EPR, electrochemistry, crystallography, among others. It is standard practice to compare spectroscopic data from enzymes to similar spectroscopic data derived from better characterized small molecules. In this way, the understanding of metalloenzymes and other metalloproteins have developed. In many cases, the small molecule analogs were created for other reasons; however, it has been increasingly common for groups to intentionally make small molecule analogs also known as enzyme mimics. These enzyme mimics are prime examples of bioinorganic chemistry.