Cofactors and Coenzymes

In many cases, enzymes require additional molecules—called cofactors—to function. These helper molecules can either be classified as metallic ions or organic, non-protein molecules. 

For example, during the first step of glycolysis, the cofactor magnesium binds to ATP, tightening the bond between two of the phosphate groups. This action allows the last phosphate group to be more easily released by the enzyme hexokinase, transforming glucose into glucose 6-phosphate. Therefore, magnesium, as a cofactor, binds to and increases the efficiency of the ATP. 

The other subset of cofactors—coenzymes—are organic compounds, usually derivatives of vitamins.  

For instance, Vitamin C is an important coenzyme in the synthesis of the protein collagen. When a hydroxylase binds to collagen, Vitamin C facilitates the hydroxylation of residues on the collagen. With the help of Vitamin C, the hydroxylase promotes the change in the shape of the collagen to its final triple helical structure, which is essential to the maintenance of important body tissues.