Enzymes are protein molecules in cells which work as catalysts. Enzymes speed up chemical reactions in the body, but do not get used up in the process.
Almost all biochemical reactions in living things need enzymes. With an enzyme, chemical reactions go much faster than they would without the enzyme.
The substances at the start of the reaction are called substrates. The substances at the end of the reaction are the products. Enzymes work on the substrates, and turn them into products.
The first enzyme was found in 1833, by Anselme Payen.
Enzymes are large molecules made from many amino acids. The amino acids link together in a long chain, which is folded up into a complex structure. Enzymes have a part which holds the substrate: a "claw, cleft, hollow or knob to grasp, hold, stretch and bend the molecule it acts on, the substrate".
There are thousands of different enzymes. Enzymes have names which show what they do. Enzyme names usually end in –ase to show that they are enzymes. Examples of this include ATP synthase. It makes a chemical called ATP. Another example is DNA polymerase. It reads an intact DNA strand and uses it as a template to make a new strand.
The general equation for an enzyme reaction is:
Substrate + Enzyme –> Substrate: Enzyme –> Product: Enzyme –> Product + Enzyme
Enzymes lower the activation energy of a reaction by forming an intermediary complex with the substrate. This complex is called an enzyme-substrate complex.
For example, sucrase, 400 times the size of its substrate sucrose, splits the sucrose into its constituent sugars, which are glucose and fructose. The sucrase bends the sucrose, and strains the bond between the glucose and fructose. Water molecules join in and make the cleavage in a fraction of a second. Enzymes have these key features:
They are catalytic. They commonly increase the rate of reaction 10 billion-fold. The enzyme itself is not changed by the reaction.
They are effective in tiny amounts. One enzyme molecule may convert 1000 molecules of substrate a minute, and some are known to convert 3 million in a minute
They are highly specific. One enzyme will only carry out one of the many reactions of which a substrate is capable.