ABSTRACT
Metals form an important component of all cellular organisms. Nearly all of the metal in living organisms is in the ion form, either bound to biomolecules or free in solution. Metal is bound via ionic or co-ordinate bonds, and metal ions in solution are often part of complexes. Metals can be divided into two broad classes: the alkali or alkali earth metals and the transition metals. Other metals, such as selenium, also play a minor role in living organisms. Metals have a wide variety of functions within living systems, including osmoregulator, structural component of tissues such as bone, protein or enzyme cofactor, and redox or electrical charge carrier. Many metals are toxic to living systems, and even some essential metals are toxic if dietary intake is exceeded.
