text: Metal ions are essential to the function of many proteins present in living organisms, such as metalloproteins and enzymes that require metal ions as cofactors. Processes including oxygen transport and DNA replication are carried out using enzymes such as DNA polymerase, which in humans requires magnesium and zinc to function properly. Other biomolecules also contain metal ions in their structure, such as iodine in human thyroid hormones.
  The uses of some of them are listed below. The list is not exhaustive, because it covers only the principal class members; others that are trace metals of especially low bioconcentration are not explored herein. Some elements that are nonmetals or metalloids (such as selenium) are beyond the scope of this article.