Enzymes: definition, types and functions

Thousands of complex chemical reactions take place within living organisms. These reactions occur in an orderly manner and in the right measure to allow life, but this would not be possible without the presence of a very special type of molecules: enzymes.

In this article we review what enzymes are, as well as the types into which we can divide them and the functions they carry out, with examples both inside and outside living organisms.

What is an enzyme?

To understand what enzymes are and what they are for, we must review some basic concepts of physics. Enzymes are biological molecules, usually proteins, that act ascatalysts for chemical reactions.

A catalyst is simply a substance that, put simply, makes it easier for a reaction to take place. Catalysts allow chemical reactions that would take a long time or need complex environmental conditions to achieve to occur in a much shorter span of timeor under more “normal” environmental conditions.

The function of enzymes is this, that of biocatalyst. This means that, inside the living beings that generate them, enzymes are facilitating complex chemical reactions, making them faster and more efficient, which allows life as we know it.

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Types of enzymes and how they work

Enzymes, as a general rule, need to bind to another molecule (called substrate), on which they will act to perform their function, which will depend on the enzyme. For this, enzymes need a binding zone, with which they recognize and bind to the substrate, in addition to the so-calledcatalytic zone, a small zone between 2 and 4 amino acids in size, which is the one that performs the enzymatic function.

The function of the enzyme, like that of other proteins, is determined by its amino acid composition. These amino acids in turn are placed in a specific form, determined by the interactions that occur between them, giving rise to the enzyme with functional capacity.

The different chains of amino acids, added to other molecules such as coenzymes, inhibitors, activators or prosthetic groups, will give rise to enzymes with different functions, which will bind to different substrates. As a general rule, we can divide enzymes according to the function they perform according to six main categories.

1. Oxidorreductasas

Oxidoreductases are enzymes that  act by facilitating the so-called redox , oxidation and reduction reactions. These reactions consist of the transfer of electrons from a donor compound to an acceptor compound.

Oxidoreductases are of enormous importance at the biological level, since they intervene in the processes of glycolysis, through which energy is extracted from sugar molecules, which are a widespread way of obtaining energy among living beings.

2. Transferases

Transferases are theenzymes responsible for transferring certain functional chemical groups from one molecule to another, such as methyls or aromatic rings. Transferases allow the creation of complex biological molecules, which could not be done at the same speed or under conditions compatible with the maintenance of life.

An important example of transferase would be Acetate-Coa transferase, a key enzyme in the proper development of the krebs cycle, a biochemical reaction related to aerobic respiration that gives us a lot of energy.

3. Hydrolases

Hydrolases are enzymes whose function is tobreak bonds between molecules through hydrolyzation, that is, the use of water molecules to facilitate the breaking of a chemical bond, which usually results in obtaining two smaller molecules from a larger molecule.

In turn, as in all these classifications, there are multiple types of hydrolases, which are divided according to the molecules on which they act. For example, there are lipases, which act on lipids, peptidases acting on amino acids or nucleotidases, which act on nucleotides.