Enzymes are proteins used by cells to catalyze reactions. A cell carries on thousands of reactions, virtually all of them regulated by enzymes, with a unique enzyme for each reaction. The central importance of enzymes is illustrated by the fact that of the estimated 100,000 genes in the human genome, almost all code for enzymes.

The unique feature of enzyme catalysts is their specificity, meaning that most enzymes can catalyze reactions involving only one set of reactants, referred to as the enzyme's substrates. In contrast, inorganic catalysts, such as platinum, tend to accelerate many different reactions. While this makes them useful in the chemistry laboratory, where the experimenter can add a select set of reactants and create a desired product, it would be disastrous in a cell, where there are many thousands of reactions possible, only a small handful of which should be running at once. Enzyme specificity gives...