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Structure of Proteins

  • Proteins are special molecules as they have fixed shapes
  • Made up of longchains of different animo acids
  • There are 21 different amino acids, so different combinations lead to different proteins
  • Proteins have 4 structures in the body:
    • Muscles & tendons
    • Hormones (eg. insulin)
    • Antibodies
    • Enzymes
  • Enzyme- A protein molecule that acts like a biological catalyst to speed up chemical reactions
  • Substrate- Reactant that fits into the active site of the enzyme
  • Active site- where the enzyme and reactant fit and react together
  • Lock and key- The substrate and enzyme bind together and the enzyme splits the substrate
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Enzymes in digestion

  • As temperature increases, the rate of digestion increases as the enzymes have more energy
  • The wrong pH and/or temperature canchange the shape of the active site so the substrate can no longer fit
  • Enzymes work best in acidic conditions


  • Breaks down carbs
  • Makes sugars
  • Found in the small intestine


  • Breaks down proteins
  • Makes animo acids
  • Found in the small intestine and stomach
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Digesting Fats


  • Fats are digested by the enyzme lipase
  • Lipase is found in the mouth, stomach and pancreas
  • Fats (lipids) are broken down into glycerol and fatty acids


  • Bile is an alkaline fluid produced by the liver
  • It neutralises acids
  • It also emulsifies fats- breaks them down into smaller droplets
  • This is so the fat has more surface area to be digested faster
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Uses of Enzymes


  • They may contain protease and lipase
  • Break down stains and work at lower temperatures, so are cheaper
  • Protease, carbohydrase and isomerase are used in the food industry
  • Enzymes can be used to diagnose and treat diseases
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