Enzyme

An enzyme is a biological molecule—typically a protein—that accelerates chemical reactions without being consumed by them. Each type of enzyme works in a specific way: it binds a single substance or group of similar substances called a substrate.

The survival of cells depends on enzymes. Most reactions, if attempted without enzymes, would proceed too slowly to be useful to the cell. Enzymes do not create new reactions that are impossible; they only lower the activation energy required to begin a reaction.

How they work

Each enzyme has a particular region called the active site. The substrate fits there, like a key in a lock, and then the reaction occurs. Once the product leaves, the enzyme is freed and can perform the task again. This is why a small number of enzymes can catalyse many reactions.

Factors that affect them

Temperature and pH level have a strong effect. Each enzyme has a temperature and pH at which it works best. Excessive heat damages the shape of the protein—a process called denaturation—and the enzyme loses its function. Many enzymes also require cofactors, such as minerals (coenzymes) or organic molecules (coenzymes) that often come from vitamins.

Classification and naming

The names of most enzymes end in '-ase', for example lactase, which breaks down the sugar in milk, and amylase, which breaks down starch. There is also an international classification system that divides enzymes into groups based on the type of reaction they accelerate, with sixty-six major classes defined.

Uses

Enzymes are used in industry and medicine. Applications include the manufacture of cheese and fermented foods, laundry detergents that break down dirt in fabrics, and diagnostic tests. Many drugs also work by inhibiting a specific enzyme in the body or in a pathogen.