3.1 Proteins, catalysts and enzymes
Protein molecules are made up of long chains of amino acids. Proteins act as structural components of tissues, as hormones, as antibodies and as catalysts.
Catalysts increase the rate of chemical reactions without changing themselves.
Enzymes are biological catalysts, and proteins. The amino acid chains are folded to form the active site.
The shape of an enzyme is vital for its function. This shape has an area where other molecules can fit - the "active site".
The substrate in a reaction can be held in the active site and either be connected to another molecule or broken down.
DIAGRAM OF FIGURE 3:
3.2 Factors affecting enzyme action
The chemical reactions that take place in living cells happen at relatively low temperatures.
The rate of enzyme-controlled reactions increase with an increase in temperature, as the molecules move around more quickly and so collide with each other more often, and with more energy.
However, after 40C the protein structure of the enzyme is affected and the shape of the active site is changed. The enzyme has been denatured.
Each enzyme works best at a particular pH value - if the conditions are too acidic or alkaline for the enzyme, the active site could change, and the enzyme becomes denatured.
3.3 Enzymes in Digestion
Digestive enzymes are made by glands in the digestive system. They work outside the body cells in the cavity of the digestive system -
Amylase (a carbohydrase):
- produced by the salivary glands, the pancreas and the small intestine
- catalyses the digestion of starch into sugars in the mouth and small intestine
- produced by the stomach, the pancreas and the small intestine
- catalyses the breakdown of proteins into amino acids
- produced by the pancreas and small intestine
- catalyses the breakdown of lipids to fatty acids and glycerol
Stomach enzymes work best in acidic conditions
3.4 Speeding up digestion
Protease enzymes in the stomach work best in acidic conditions. Glands in the stomach wall produce hydrochloric acid to create very acidic conditions.
Amylase and lipase work in the small intestine. They work best in slightly alkaline conditions.
The liver produces bile that is stored in the gall bladder. It neutralises acid and emulsifies fats.
When fat droplets are emulsified, their surface area is increased, which increases the rate of fat digestion by lipase.
3.5 Making use of enzymes
Some microorganisisms produce enzymes that pass out of their cells and can be used in different ways:
- Biological detergents contain proteases and lipases that digest food stains. They work at lower temperatures than ordinary washing powders. This saves energy and money spent on electricity.
- Proteases are used to predigest proteins in some baby foods
- Isomerase is used to convert glucose into fructose syrup. Fructose is much sweeter, so less is needed in foods. The foods, therefore, are not so fattening.
- Carbohydrases are used to convert starch into sugar syrup for use in foods.
- In industry, enzymes are used to bring about reactions at normal temperatures and pressures. Traditional chemical processes require expensive equipment.
3.6 High-tech enzymes
Advantages of using enzymes:
- enzymes in biological washing powders are effective at removing stains
- biological washing powders can be used at lower temperatures, saving energy and reducing costs
- some enzymes are used in medicine to diagnose, control or even cure diseases
- in industry, costs of equipment and energy can be reduced
- if people misuse washing powders they may have allergic reactions
- enzymes may enter waterways via the sewage system
- industrial enzymes can be costly to produce
- enzymes denature at the high temperature needed to kill pathogens in the washing
- some fabrics such as wool will be digested by protease