A description of living organisms, using simple bacterial and eukaryotic cells as examples. The cell’s metabolism is described by analogy to an automobile factory, where different components of the final automobile are made on their own assembly lines before merging to achieve the final complete car. Enzymes are compared to the individual workers who handle specific tasks along such assembly lines. Enzymes are then more specifically described as having an active site, or catalytic pocket, that has evolved to be the ideal size and shape for a substrate to bind there, so that it can be chemically altered. A brief history of enzymology is included. The importance of a cell’s pH and the concept of enzyme affinity are then explained, which is summarized as the enzyme’s KM, and illustrated by a Michaelis–Menten kinetic plot. Enzyme nomenclature is explained, and enzyme rates (speeds) are defined.