Enzymes are biological catalysts. Catalysts are materials that are able to speed up the rate of chemical reactions. One notable catalyst is the catalytic converter, a platinum catalyst installed onto vehicle exhausts which accelerates the decomposition of various exhaust products that contribute to atmospheric pollution.

Enzymes however are not composed of metals, rather they are protein chains (Figure 1). And unlike catalysts used for industrial applications, they do not require extreme conditions, such as high temperature or pressure to function, instead they function at temperatures that life exists at. Without enzymes there likely will be no life. Enzymes allow most of the reactions required by living organisms to happen. Without enzymes, most biological reactions would be too slow to take place at any reasonable timescale.

Figure 1: Cytochrome C Oxidase is an enzyme that completes the process of respiration, converting glucose and oxygen into carbon dioxide, water and cellular energy in the form of adenosine triphosphate. It is also one of the most widely studied enzymes, and had been linked to many roles and disease processes in cells.

The general structure and function of an enzyme can be described as follows: The protein that makes up the enzyme has a part of the enzyme known as the active site, this active site binds to one compound(s), known as the substrate, and through the enzyme's chemical properties, converts it to another compound(s), known as the product. The range of substrates, products, and active sites is extensive, with a single organism having thousands of enzymes catalyzing thousands of compounds. However, despite this range of functions, enzymes have some common features.

Enzymes also allow reactions to be controlled. A living organism can regulate which reactions take place by regulating which enzymes are being used at any given time. Since biological reactions will not take place without enzymes, the organism can regulate which reactions are taking place.

The study of enzymes is vital to the study of life. The presence of enzymes indicates which reactions are taking place in a lifeform, and the biological processes that it carries out during its life cycle. Enzymes are also important to study to understand disease processes, often a failure of one or more enzymes is a key factor in the development of disease, so they are targets for drug design. As enzymes may also be specific to certain lifeforms, they may also be specific targets for pesticides and antimicrobial agents.

Enymzes also have a role in industry. As they are proteins they are inherently safe for human consumption, and so have a lot of applications in the food industry. Enzymes from cow's stomachs have been used to make cheese for centuries, though in the modern era pure enzymes can be produced and used to make vegetarian cheeses. Enzymes are also used in cleaning agents. Biological laundry detergent contains enzymes that digest stains and can do so without needing high temperature washing cycles, thus making laundry washing more energy efficient.

Enzymes are also used as tools in research and scientific practice. Enzymes that catalyze reactions can be used to monitor certain biological processes that are difficult to monitor otherwise. the protein-fragment complementation assay is one such assay, using the activity of an enzyme as a way of monitoring the formation of protein interactions.

All in all, enzymes are fascinating and useful biological engines.