The word “enzyme” was coined in 1878 by German scientist Wilhelm Kuhne. It is derived from the Greek words for “leavened.” The root “zyme” means to leaven, as with dough or bread. It is observed that some chemical reactions occurred with the addition of ferments, or living organisms like yeast. But it was also noticed that some reactions occurred without the living organisms being added to the reaction. But instead it was observed that just some of their extracts catalyzed these reactions, and then came the enzymes in picture.
The basic role of an enzyme is to increase the rate of a biochemical reaction, without being actually used up. Most reactions inside cells occur almost one million times faster just because of the presence of the enzymes. Enzymes typically react with just one substrate, that is, one specific molecule type. There can be thousands of enzymes at work in one organism, each one with a vital role.
Enzymes are catalysts; they are not consumed by the reactions they bring about. Enzymes are much more specifically targeted than catalysts. Enzymes catalyze about 4000 known biochemical reactions.
All the known enzymes are classified in six basic groups. These categories are organized according to the working of the enzyme on a molecular level.
These classes are:
1. Oxidoreductases
2. Transferases
3. Hydrolases
4. Lyases
5. Isomerases
6. Ligases
Oxidoreductases are the enzymes that catalyze oxidation or reduction reactions. These reactions involve the transfer of electrons from one molecule or the reductant to another molecule or the oxidant. These reactions are vital to life for their role in essential metabolic processes like glycolysis, which occurs in nearly every organism.
Transferase is the enzymes that catalyze the transfer of a functional group (such as methyl) from one molecule to another. The first molecule is called the donor and the second molecule is called the acceptor. These transfer processes are some of the most basic and vital reactions in life.
Hydrolases are the enzymes that bring about the hydrolysis, which is the breaking of chemical bonds with the addition of water molecule. There is a wide variety of identified hydrolases, over 200 of them, from those that break down proteins to those that cleave ester bonds. Exohydrolase enzymes cut the molecules at the end of the chain, and endohydrolase enzymes do so in the middle of the chain.
Lyases are the enzymes that catalyze lysis reactions. Lysis reactions are the kind of elimination reactions that are not hydrolytic or oxidative. The lyases are also sometimes called synthase enzymes. A Michael addition, the reverse reaction, is also possible. However, two substrates are required for the reverse reaction to happen, whereas one substrate is required for the lysis reaction. This makes lyases unique among enzymes.
Isomerase are the enzymes that catalyze structural changes within a molecule, this brings about a change in shape since there is only one substrate and one product with nothing gained or lost. Within this category, there are a few sub-categories depending upon their working. There are geometric, structural, enantiomer, and stereoisomer isomerases.
Ligases enzymes carry out the ligation reactions. Ligation occurs when two substrates are being joined together. Chemical potential energy is usually required for this reaction to occur, so it is often paired with the hydrolysis of a diphosphate bond. DNA ligase, which catalyzes the ligation or the repair of the breaks in DNA, is an example of this category enzyme.

Catalysis makes the crucial metabolic processes of life possible. Catalysts are substances that bring about the acceleration of chemical reactions but themselves remain unchanged and unused up in the chemical process. Enzymes are the catalysts that make the speed and processes of life possible.