Biology GCSE


  • Created by: Anna Fox
  • Created on: 04-03-12 13:18

Proteins and enzymes

Proteins are made from long chains of smaller molecules named amino acids. These long chains are folded into particular shapes. This is important in relation to how antibodies and enzymes work.

Amino acids and proteins: Proteins are like polymers (a large molecule formed from many identical smaller molecules) they are built up in cells when monomers called aminio acids join together end to end.

Different proteins: The long chains of amino acids fold to give each type of protein molecule a specific shape, proteins act as: Structual components: of tissue (such as muscles) Hormones (such as insulin) Antibodies (part of the bodys immune system) Biological catalyst (enzymes)

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How enzymes work

Enzymes are biological catalysts - substances that increase the rate of chemical reactions without being used up. Enzymes are proteins folded into complex shapes that allow smaller molecules to fit into them. The place where these substrate molecules fit is called the active site.

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Other substances in digestion

Stomach acid

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, at a low pH.


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. Bile is produced by the liver and stored in the gall bladder.

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Digestive enzymes

The enzymes involved in respiration, photosynthesis and protein synthesis work inside cells. Other enzymes are produced by specialised cells and released from them.

Different enzymes catalyse different digestion reactions:

Amylase Starch → sugars Protease Proteins → amino acids Lipase Lipids → fatty acids + glycerol

Overall, this means that:

  • 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
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Enzymes in the home industry

Uses of enzymes:

Protease: Used to pre-digest proteins during the manufacture of baby foods. Lipase: used together with protease- in biological detergents to break down the substances into smaller, water soluble substances.  

Carbohydrase: Used to convert starch syrup, relativly cheap to do.

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

In industry, enzymes allow reactions that normally need expensive, energy-demanding equipment to happen at normal temperatures and pressures. On the other hand, most enzymes are denatured at high temperatures. Many enzymes are expensive to produce.

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