Biological Molecules

• The three chemical elements:

  1. Carbohydrates: Carbon, Hydrogen and Oxygen
  2. Proteins: Carbon, Hydrogen, Oxygen and nitrogen
  3. Lipids: Carbon, Hydrogen and Oxygen
• Structure of Carbohydrates, Proteins and Lipids:

  • Carbohydrates: Simple sugars such as glucose and fructose join together to make substances such as Maltose, Sucrose, Starch, Glycogen or cellulose
  • Lipids: Made up of three fatty acids bonded to a glycerol molecule
  • Proteins: Made up of amino acids bonded together
• The shape of the protein affects its function
• Preparing a food sample:

  1. Take food sample and crush with pestle & mortar
  2. Place crushed up food sample in a test tube
  3. Add distilled water to the test tube and mix with a rod
  4. Filter the mixture
• Testing for glucose:

  1. Add Benedict's solution to the food sample test tube
  2. Heat in water bath for 5 minutes
  3. If glucose is present, solution should turn from blue to orange
• Testing for starch:

  1. Add iodine solution to the test tube
  2. If starch is present, solution should turn from orange to blue-black
• Testing for protein:

  1. Add Biuret solution
  2. If proteins are present, solution should turn from blue to lilac
• Test for lipids:

  1. Add sudan III stain solution to the test tube
  2. If lipids are present, a red ring should form on top of the solution
• Enzymes are biological catalysts that speed up the rate of chemical reactions without being used up. They are biological because they are produced in living cells
• Enzymes are specific to one particular substrate:

  • The enzymes and substrates will move randomly in the solution
  • When an enzyme and its complementary substrate collide, an enzyme-substrate complex is formed and the reaction occurs
  • A product is formed from the substrate which is released from the active site
• Effect of temperature on enzymes

  • Optimum temperature means the molecules move faster and there will be more collisions leading to enzyme-substrate complexes
  • Low temperatures do not denature enzymes
  • High temperatures beyond the optimum will break the bonds holding the enzyme together as the active site changes shape
• Effect of pH on enzyme activity

  • If the pH is too high or low, the bonds holding the amino acid chain together which make the proteins will be disrupted
  • This changes the shape of the active site
• Investigating effect of temperature on enzyme activity (part 1)

  1. Add 5cm3 of starch solution to a test tube

  2. Heat to a set temperature in a beaker of water and Bunsen burner

  3. Take a spotting tile and add a drop of iodine to each tile

  4. Add 2cm3 of amylase solution to the test tube using a syringe and mix well
• Investigating effect of temperature on enzyme activity (part 2)

  1. Every minute
 add a droplet of the solution to a spotting tile with the iodine solution
  2. Repeat until the spotting tiles will stop turning blue-black
  3. Record the time taken for the tiles to stop turning blue-black
  4. Repeat for a range of different temperatures
• Investigating the effect of pH on enzyme activity:

  1. Take a spotting tile and add a drop of iodine to each tile
  2. Place 2cm3 of amylase into a test tube
  3. Add 1cm3 of buffer solution to the test tube (pH 2)
  4. Add 2cm3 of starch solution to the amylase and buffer solution and mix it together
  5. Start the stop watch and every 10 seconds, transfer a drop of the solution to one of the tiles (they should turn blue-black)
  6. Repeat until the iodine solution will no longer turn blue-black
  7. Record the time taken for this to happen
  8. Repeat for different pHs of buffer solution