Enzymes

Enzymes are usually large long-chain protein molecules that act as a catalyst for chemical reactions in the body. A catalyst is a material that speeds up a chemical reaction but is itself unchanged at the end of the reaction. Very small amounts of catalysts and enzymes can affect large quantities of reactants. They can, however, be poisoned if the conditions are changed and become unfavourable, or an impurity is present. Enzymes, being proteins, like to work at a set and narrow range of temperatures, and if they are warmed above their working temperature they become inactive due to being de-natured.

Enzymes cannot perform reactions that would not normally take place, they simply speed them up. One of the key features of enzymes is their characteristic and specific shape. One enzyme does not work with another reaction because the reactant and enzyme interlock and this depends upon their mutual matching shapes.
Enzymes are usually specific to one type of reaction.

Catalase is one of the vital enzymes carried around in very small quantities in the blood. It destroys the harmful effects of any peroxide molecules or ions being produced accidentally when glucose is oxidized. If it was not destroyed this would cause much harm to many of the body’s systems, including destroying the DNA of
cells. The peroxide is converted into the harmless materials of water and oxygen gas:

2H2O2 --> 2H2O + O2

Another useful enzyme is amylase, found in the saliva and the small intestine. It has a role in the digestive system, breaking down the starches (carbohydrates) in foods into maltose. This is then acted upon by a further enzyme, maltase, to convert the maltose into glucose. Humans can digest the starch in potatoes but the enzymes do not break down the chemically similar substance, cellulose, into glucose. Thus humans cannot digest the cellulose in grass, but the enzymes in the digestive systems of cows and sheep breaks it down.
The human stomach and small intestine also contain enzymes that help in the hydrolysis and break-down of proteins, first into shorter chain peptides (this is done with the aid of the enzymes pepsin and trypsin), and then hydrolysed further into individual amino acids with the help of the enzyme peptidase. Any fats in food are
also hydrolysed in the stomach with the aid of lipase enzyme to form fatty acids (carboxylic acids).
It can be seen that the break-down of the components of food is greatly speeded up with the aid of enzymes, which make the smaller units of glucose, amino acids and fatty acids available for transport to cells for synthesis into body-building materials.