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ENZYMES 

Enzymes are protein molecules that help chemical reactions in living organisms to take place. The term enzyme has a specific meaning: an enzyme is a biological catalyst that speeds up the rate of a chemical reaction without being used up in the chemical reaction itself. Let us analyse this definition in greater detail.

Biological: Enzymes are protein molecules which are made of long chains of amino acids. These fold into unique three-dimensional structures with a region known as an active site where reactions take place.

Catalyst: Enzymes speed up chemical reactions without being used up in the reaction themselves. All chemical reactions require a certain minimum amount of energy to take place. This energy is known as the free energy of activation. Enzymes lower the energy of activation thus speeding up chemical reactions 

Figure 1. Enzymes lower the activation energy, thus making reactions occur faster.

Enzymes are not consumed by the reactions they catalyse: they do not alter the equilibrium of reactions, thus they catalyse both forward and reverse reactions. The direction in which a reaction proceeds is determined by concentration of the substrates and the products of the reactions.

Enzymes may be involved in reactions that break down or build up molecules. The breakdown reactions are known as catabolic reactions. The building up reactions are known as anabolic reactions.