The relationships between molecular structures and biological activities are at the center of interest for biochemists. To understand the properties of molecular structures, they have engaged with chemistry; biological activity can only be understood if they have also analyzed cellular structures and their functions. While a description of individual physiological phenomena was possible hundreds or even thousands of years ago, only recent advances in chemistry, cell biology, and genetics have made an understanding of molecular mechanisms possible. From this perspective, the concepts of biocatalysts, the alpha-helix of proteins, or the double helix of nucleic acids may be old for a student who has delved into biochemistry, but they are quite young when compared to other established sciences.