enzyme

Enzymes are catalysts that can help break larger molecules into smaller molecules while remaining unchanged themselves. Like a key for a lock, each enzyme is specific to one molecule. Most also function best within a narrow temperature and pH range. As the temperature rises enzymes catalyse more molecules but beyond a certain temperature most enzymes become denatured.

Biological catalyst produced in cells, and capable of speeding up the chemical reactions necessary for life. Most enzymes are large, complex proteins, usually soluble, and are highly specific, each chemical reaction requiring its own particular enzyme. The enzyme's specificity arises from its active site, an area with a shape corresponding to part of the molecule with which it reacts (the substrate). The shape of the enzyme where the chemical binds only allows the binding of that particular chemical, rather like a specific key only working a specific lock (the lock and key hypothesis). The enzyme and the substrate slot together forming an enzyme–substrate complex that allows the reaction to take place, after which the enzyme falls away unaltered.

The activity and efficiency of enzymes are influenced by various factors, including temperature and acidity (pH). Temperatures much highter than those to which the organism of origin is adapted damage (denature) the intricate structure of enzymes, inactivating them and causing reactions to stop. Each enzyme operates best – at its maximum rate – within a specific pH range and temperature, and is denatured by excessive acidity or alkalinity or extremes of temperature.

In digestion, digestive enzymes include amylases (which digest starch), lipases (which digest fats), and proteases (which digest protein). Other enzymes play a part in the conversion of food energy into ATP, the manufacture of all the molecular components of the body, the replication of DNA when a cell divides, the production of hormones, and the control of movement of substances into and out of cells.

Enzymes have many uses in medical and industrial biotechnology, from washing powders to drug production, and as research tools in molecular biology. They are involved in the making of beer, bread, cheese, and yogurt. They can be extracted from bacteria and fungi and genetic engineering now makes it possible to tailor an enzyme for a specific purpose.

The most abundant enzyme is ribulose biphosphate carboxylase. It is found in chloroplasts and is associated with photosynthesis.

Certain RNA molecules can also act as enzymes; these are known as ribozymes.