What are enzymes and what are some of their functions?

What are enzymes?

Enzymes are biological catalysts that have many functions both inside and outside cells.

Catalysts increase the rate of chemical reactions. Biological catalysts are called enzymes.

Enzymes are protein molecules made up of long chains of amino acids. These long chains are folded to produce a special shape
which enables other molecules to fit into the enzyme. This shape is vital for the enzymes function. High temperatures destroy this special shape.

Different enzymes work best at different pH values.

Enzymes inside living cells catalyse processes such as respiration, protein synthesis and photosynthesis.

How does our body produce the energy it needs?

During aerobic respiration (respiration which uses oxygen) chemical reactions occur which: use glucose (a sugar) and oxygen release energy.
Most of the reactions in aerobic respiration take place inside mitochondria.

Aerobic respiration is summarised by the equation:

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

The energy that is released during respiration is used:
− to build up larger molecules using smaller ones
− in animals, to enable muscles to contract
− in mammals and birds, to maintain a steady body temperature in colder surroundings
− in plants, to build up sugars, nitrates and other nutrients into amino acids which are then built up into proteins.

How and where is our food digested?

Enzymes inside living cells catalyse the reactions that build up amino acids and proteins

Some enzymes work outside the body cells. The digestive enzymes are produced by specialised cells in glands and in thelining of the gut. The enzymes then pass out of the cells into the gut where they come into contact with food molecules. They catalyse the breakdown of large molecules into smaller molecules:

− the enzyme amylase is produced in the salivary glands, the pancreas and the small intestine. This enzyme catalyses the breakdown of starch into sugars in the mouth and small intestine
− protease enzymes are produced by the stomach, the pancreas and the small intestine. These enzymes catalyse the breakdown
of proteins into amino acids in the stomach and the small intestine
− lipase enzymes are produced by the pancreas and small intestine. These enzymes catalyse the breakdown of lipids (fats and oils) into fatty acids and glycerol in the small intestine

− the stomach also produces hydrochloric acid. The enzymes in the stomach work most effectively in these acid conditions
− the liver produces bile which is stored in the gall bladder before being released into the small intestine. Bile neutralises the acid that was added to food in the stomach. This provides alkaline conditions in which enzymes in the small intestine work most effectively.

Can we use enzymes to do other things?

Some micro-organisms produce enzymes which pass out of the cells. These enzymes have many uses in the home and in industry.

In the home, biological detergents may contain protein-digesting and fat-digesting enzymes (proteases and lipases).

In industry:
− proteases are used to pre-digest the protein in some baby foods
− carbohydrases are used to convert starch into sugar syrup
− isomerase is used to convert glucose syrup into fructose syrup, which is much sweeter and therefore can be used in smaller quantities in slimming foods.