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Enzymatic Reactions

Enzymatic Reactions

Enzymes (or biocatalysts) are one of the most important proteins formed within living cells because they act as biological catalysts to speed up chemical reactions. Thousands of enzymes reside in a single cell, each one a catalyst that facilitates a specific chemical reaction. Without enzymes, reactions would occur in a random and indiscriminate manner. The lock-and key concept describes enzyme action. An enzyme combines with a substance, called a substrate, catalyzing or speeding up a reaction, which releases a product. The enzyme is freed unchanged after the reaction and is able to react with another substrate, yielding another product.

Enzyme Nomenclature

The names of most enzymes end in -ase. Enzymes are usually named after the substrate they act upon or the resulting type of chemical reaction. For example, sucrase is the enzyme that acts on sucrose, and lactase is the enzyme that breaks down lactose to glucose and galactose. This general nomenclature rule does not always apply; the enzyme papain is named after papaya, from which it is derived, and ficin gets its name from figs. These enzymes, obtained from fruits, are used in meat tenderizers to break down meat’s surface proteins.

Structure of Enzymes

The overall structure of an enzyme, called the holoenzyme, contains both a protein and non-protein portion. Most of the enzyme is protein, but the nonprotein portion, which is necessary for activity, is either a coenzyme (usually a vitamin) or a cofactor (usually a mineral).


Substrate – A substance that is acted upon, such as by an enzyme.

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