enzymes

• Enzyme


  Speeds up chemical reactions by having a groove on their surface called the active site
• Substrate


  The molecule that the enzyme reacts with, fits perfectly into the active site
• Lock and key theory

  The substrate must fit perfectly into the active site
• Effect of temperature on enzyme activity

  1. Gradually increase temperature

  2. Measure enzyme activity (rate of reaction)

  3. Activity increases as temperature increases

  4. Reach optimum temperature

  5. Activity rapidly decreases past optimum temperature
• Optimum temperature


  The temperature at which the enzyme is working at the fastest possible rate, maximum frequency of successful collisions between substrate and active site
• Denaturation


  At high temperatures, the enzyme molecule vibrates and the shape of the active site changes, so the substrate no longer fits perfectly
• Effect of pH on enzyme activity

  1. Alter pH

  2. Measure enzyme activity (rate of reaction)

  3. Enzyme has an optimum pH where activity is maximum

  4. Activity drops to zero if pH is too acidic or too alkaline
• Optimum pH


  The pH at which the enzyme works best
• Enzymes with different optimum pH

  • Protease enzyme in stomach (acidic pH)
  • Lipase enzyme from pancreas (alkaline pH)
• Carrying out chemical tests for carbohydrates, proteins and lipids

  1. Grind food sample with distilled water using mortar and pestle to make a paste

  2. Transfer paste to beaker and add more distilled water

  3. Stir to dissolve chemicals

  4. Filter solution to remove suspended food particles
• Carbohydrates

  Include starch and sugars such as glucose
• Test for starch

  1. Place 2cm3 of food solution in test tube

  2. Add a few drops of iodine solution

  3. Blue-black colour indicates presence of starch
• Test for sugars (e.g. glucose)

  1. Place 2cm3 of food solution in test tube

  2. Add 10 drops of Benedict's solution

  3. Heat test tube in hot water bath for 5 minutes

  4. Colour change indicates amount of reducing sugars present
• Benedict's test

  Only works for reducing sugars, not non-reducing sugars like sucrose
• Test for proteins

  1. Place 2cm3 of food solution in test tube

  2. Add 2cm3 of Biuret solution

  3. Purple/lilac colour indicates presence of proteins
• Test for lipids/fats

  1. Grind food with distilled water using mortar and pestle (do not filter)

  2. Transfer 2cm3 of solution to test tube

  3. Add a few drops of distilled water and ethanol

  4. Shake gently

  5. White cloudy emulsion indicates presence of lipids
• All chemicals used in these tests are potentially hazardous, so safety goggles must be worn
• Ethanol is highly flammable, so no naked flames should be present