Enzymes are biological catalysts - catalysts are substances that increase the rate of chemical reactions without being used up. Enzymes are proteins that are folded into complex shapes - smaller molecules fit into them. The molecules fit in the active site.

If the shape of the enzyme changes, its active site may no longer work. The enzyme has been denatured. They can be denatured by high temperatures or extreme pH. The enzyme has not been killed. Enzymes are made by living things, they are proteins, and not alive.

Enzymes in cells catalyse photosynthesis, protein synthesis - joining amino acids together, and aerobic respiration.

Respiration is a chemical process in which energy is released from food substances, such as glucose. Areobic respiration needs oxygen to work. Most of the chemical reactions involved in the process happen in mitochondria.              

 Glucose + oxygen    →    carbon dioxide + water (+ energy)

Digestion is the breakdown of large molecules into smaller, soluble molecules that can be absorbed into the body. Digestion happens inside the gut, and relies on enzymes.

The enzymes involved in respiration, photosynthesis and protein synthesis work inside cells. Other enzymes are produced by specialised cells and released from them; the digestive enzymes are like this. They pass out into the gut, where they catalyse the breakdown of food molecules.

Enzyme    Reaction Catalysed

Amylase   Starch    →    Sugars

Protease Proteins    →    Amino Acids

Lipase      Lipids    →    Fatty acids + Glycerol

Amylase is an example of a carbohydrase. Lipids are fats and oils.

Different parts of the gut produce different enzymes.

Enzyme    Where Produced

Amylase   Salivary Glands, Pancreas, Small Intestine

Protease  Stomach, Pancreas, Small Intestine

Lipase       Pancreas, Small Intestine

*Amylase Catalyses the breakdown of starch into sugars in the mouth and small intestine.
*Proteases Catalyse the breakdown of proteins into amino acids in the stomach and small intestine.
*Lipases Catalyse the breakdown of fats and oils into fatty acids and glycerol in the small intestine.

Enzymes in the stomach

The stomach produces hydrochloric acid. This helps to begin digestion, and it kills many harmful microorganisms that might have been swallowed along with the food. The enzymes in the stomach work best in acidic conditions - in other words (Low pH).

Enzymes in the Small Intestine

After the stomach, food travels to the small intestine. The enzymes in the small intestine work best in alkaline conditions, but the food is acidic after being in the stomach. A substance called bile neutralises the acid to provide the alkaline conditions needed in the small intestine.

Lipase - breaks down fats, Protease - breaks down proteins, Carbohydrase - breaks down carbohydrates. Enzymes allow certain industrial processes to be carried out at normal temperatures and pressures. Enzymes are also used in the home eg. Biological detergents.

Enzyme  Use

Protease Used to pre-digest proteins during the manufacture of baby foods

Lipase Used - together with protease - in biological detergents to break down - digest - the substances in stains into smaller, water soluble substances

Carbohdrydrates Used to convert starch syrup, which is relatively cheap, into sugar syrup, which is more valuable - for example, as an ingredient in sports drinks

Isomerase Used to convert glucose syrup into fructose syrup - fructose is sweeter than glucose, so it can be used in smaller amounts in slimming foods