All reactions relevant to biology belong to one of the two groups: those with a kinetic barrier and those with a thermodynamic barrier. The kinetic barrier can be overcome by employing a catalyst. Reactions with a thermodynamic barrier (uphill, endergonic reactions) require the provision of energy (such as ATP hydrolysis) in addition to a catalyst. Regardless of the nature of barriers faced—greater than 99% of all the reactions occurring in biological systems are catalyzed. With the minor exception of a few RNA catalysts (ribozymes) all the enzymes are built from a protein scaffold. These catalysts par excellence are at the very foundation of life. The three hallmark features of these biocatalysts are—Catalysis, Specificity, and Regulation.