U

enzyme

noun Biochemistry.

any of various proteins, as pepsin, originating from living cells and capable of producing certain chemical changes in organic substances by catalytic action, as in digestion.

noun

any of a group of complex proteins or conjugated proteins that are produced by living cells and act as catalysts in specific biochemical reactions

1881, as a biochemical term, from German Enzym, coined 1878 by German physiologist Wilhelm Kühne (1837-1900), from Modern Greek enzymos “leavened,” from en “in” (see en- (2)) + zyme “leaven” (see zymurgy).

Any of numerous proteins or conjugated proteins produced by living organisms and functioning as specialized catalysts for biochemical reactions.

Any of numerous proteins produced in living cells that accelerate or catalyze the metabolic processes of an organism. Enzymes are usually very selective in the molecules that they act upon, called substrates, often reacting with only a single substrate. The substrate binds to the enzyme at a location called the active site just before the reaction catalyzed by the enzyme takes place. Enzymes can speed up chemical reactions by up to a millionfold, but only function within a narrow temperature and pH range, outside of which they can lose their structure and become denatured. Enzymes are involved in such processes as the breaking down of the large protein, starch, and fat molecules in food into smaller molecules during digestion, the joining together of nucleotides into strands of DNA, and the addition of a phosphate group to ADP to form ATP. The names of enzymes usually end in the suffix -ase.

A protein molecule that helps other organic molecules (see also organic molecule) enter into chemical reactions with one another but is itself unaffected by these reactions. In other words, enzymes act as catalysts for organic biochemical reactions.