Metals catalyze numerous biological processes and serve as cofactors for several key enzymes. In fact, it has been estimated that nearly half of all enzymes utilize metals to enable their structural integrity and functional role. For instance, the heme-copper complex in cytochrome c oxidase binds molecular oxygen and facilitates four-electron reduction of oxygen to water during respiration (Figure top panel) and the heme-iron cofactor in myoglobin/hemoglobin proteins enables transfer and storage of oxygen (Figure bottom panel). Similarly, plants use calcium and manganese cofactors to catalyze the oxidation of water during photosynthesis (Figure Metal cofactors critical in biological processes in plants. Calcium-manganese cluster of photosystem (II) (PDB: 4UB6) which is involved in lightdependent photosynthesis is shown at the top, while iron-molybdenum cluster in nitrogenase (PDB: 1M1N) responsible for reduction of nitrogen to ammonia is shown at the bottom. Chemical equations corresponding to each biological process are also shown at the bottom of each panel.