Enzymes are mainly proteins, that catalyze (i.e., increase the rates of) chemical reactions. In enzymatic reastions, the molecules at the beginning of the process are called substrates, and the enzyme converts them into defferent molecules, called the products. Almost all processes in a biological cell need enzymes to occur at significant rates. Since enzymes are selective for their substrates and speed up only a few reactions from among many possibilities, the set of enzymes made in a cell determines which metabolic pathways occur on that cell. |
