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  • Created by: Hope
  • Created on: 17-04-14 16:52


Protiens are made of long chains of smaller molecules calle amino acids.These long chains are folded to produce a specific shake that enables other molecules to fit into the protien. If the shape was to change it would no longer work and become denatured.

Protiens are polymers. They are built up in cells when monomers called amino acids join together.

Protiens act as:

  • Structural componenets of tissues such as muscles
  • Hormones
  • Antibodies 
  • Catalysts

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

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How Enzymes Work

On every enzyme there is an 'active site' this is where the substrate molecules fit for the two molecules to join together and form a reaction.

The substrate has a complementary shape that fits the active site. 

If the shape of the enzyme changes, its active site may no longer work. We say the enzyme has been 'denatured'.

Enzymes can be denatured by high temperatures or extremes of pH. Note that it is wrong to say the enzyme has been killed. Although enzymes are made by living things, they are proteins and not alive.

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Temperature, PH and Enzymes

Temperature and enzymes -

As the temperature increases so does the rate of reaction but very high temperatures denature the enzymes and the shape will change. Enzymes like to work (and by work I mean the enzyme is more likely to find the substrate) at 37 degrees (which is its optimum temperature) thats why a humans body temperature is 37 degrees.

PH and enzymes - 

All enzymes like to work at different PH's, their optimum PH depends on where they usually work. e.g. intestinal enzymes have a ph of 7 and stomach enzymes have a ph of 2

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Enzymes in digestion

  • Amalayse breaks down starch (carbohydrates) into sugars/glucose
  • Protease breaks down protiens into amino acids
  • Lipase breaks down lipids (fats) into fatty acids and glycerol 

Amalayse is produced in the salivary glands, the pancreas and small intestine. This enzyme catalyses the breakdown of starch into sugars in the mouth and small intestine 

Protease is produced by the sotmach, in the pancreas and small intestine. These enzymes catalyse the break down of protiens into amino acids in the stomach and the small intestine.

Lipase enzymes are produced by the pancreas and small instetine. These enzymes catalyse the break down of lipids into fatty acids and glycerol in the small intestine.

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Other substances in digestion

The purpose of digestion is to break down large, insoluable molecules into smaller soluable molecules. (soluable means can be dissolved into water)

Stomach Acid- 

The stomach produces hydrocholoric acid. This helps to begin the digestion because the it kills any harmful microorganisms that might have been swallowed along with the food and enzymes in the stomach work best in acidic conditions (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.

Bile also emulsifiys fats and oils, so keeps things mixed up e.g. water and oil

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Enzymes in the home and industry

Lipase - Breaks down fats

Protease - Breaks down protiens 

Carbohydrase - Breaks down carbohydrates

Uses of enzymes in industry-

  • Baby food - Protease pre-digests protiens during the manufacture 
  • Biological Detergents - Both lipase and protease are used to break down the substances in stains into smaller, water soleubale substances
  • Sugar Syrup- Plants make glucose and store it as starch we take the starch and use carbohydrase to turn it back to glucose to make sugar
  • Fructose Syrup - Good slimming food, use isomerase to turn the glucose syrup into fructose. 
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Advantages and Disadvantages of Enzymes in the hom


  • They work at low temperatures
  • Work at low pressures
  • Efficent catalysts 
  • Process  is often cheaper to run


  • Can be denatured by high temperatures
  • Sensitive to changes in ph
  • Purified enzymes can be expensive to produce
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