Enzymes-Biology-AQA Additional Science

Information on enzyme structure, factors affecting enzyme action, aerobic respiration, enzymes in digestion, speeding up digestion and making use of enzymes.

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  • Created by: Rukhsar
  • Created on: 10-04-10 17:49

Enzyme structure

Enzymes are biological catalyst which speed up reactions.

Enzymes are large proteins and each has a unique shape. The shape has to fit into other molecules. This area is called the 'active site'.

If the temperature gets too high the enzymes shape will change and will no longer work. This means that the enzyme has denatured or is destroyed. It has not died.

Enzymes can catalyse the build up of small molecules into large molecules or the break down of large molecules into small molecules.

Enzymes lower the amount of energy necessary for a reaction to take place - the 'activation' energy.

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Factors affecting enzyme action

If the temperature is warm, reactions take place faster. If the temperature is high the molecules move around more quickly meaning the molecules collide with each other more often and with more energy.

However, if the temperature gets too high then the enzyme stops working. This is because the active site changes its shape and the enzyme becomes denatured.

In certain acidic or alkaline conditions the enzyme works best. If the pH is too acidic or alkaline for the enzyme, then the active site could change shape. The enzyme would stop working.

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Aerobic respiration

Aerobic respiration is the release of energy from food when oxygen is available. The equation for respiration is:

glucose + oxygen --------> carbon dioxide + water [+ energy]

The process mostly takes place in the mitochondria.

The energy released is used to:

  • build larger molecules from smaller ones
  • enable muscle contraction in animals
  • maintain a constant body temperature in mammals and birds
  • build sugars, nitrates and other nutrients in plants into amino acids and then proteins
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Enzymes in digestion

Digestion is the breakdown of large, insoluble molecules into smaller soluble molecules.

  • Amylase (a carbohydrase) converts starch into simple sugars. It is made in three places the salivary gland, the pancreas and the small intestine.
  • Protease converts proteins into amino acids. It is made in three places the stomach (pepsin), the pancreas and the small intestine.
  • Lipase converts lipids (fats and oils) into glycerol and fatty acids. It is made in two places the pancreas and the small intestine.

Without enzymes, digestion would be too slow.

There are specific conditions in different parts of the gut that help enzymes to work effectively.

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Speeding up digestion

  • Protease enzymes in the stomach work best in acid 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 when the conditions are slightly alkaline.
  • The liver produces bile that is stored in the gall bladder. bile is squirted into the small intestine and neutralises the stomach acid. It makes the conditions slightly alkaline.

Enzymes only work well within a narrow pH range

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Making use of enzymes

Enzymes can be used in products in the home and in industry. Microorganisms produce enzymes that we can use.

Biological washing powders contain enzymes that digest food stains. They work at lower temperatures than ordinary washing powders so can save us money. We also use:

  • Protease enzymes to pre - digest proteins in some baby foods
  • Isomerases to convert glucose into fructose. Fructose is much sweeter, so less is needed in foods. The foods, therefore, are not so fattening.
  • Carbohydrases to convert starch into sugar syrup for use in foods
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