chap 3: biologial molecules

• carbohydrates made up of carbon, hydrogen, oxygen
• glucose is a simple sugar
• fructose is a simple sugar
• maltose is a double sugar
• sucrose is a double sugar
• starch is a complex carbohydrate
• cellulose is a complex carbohydrate
• glycogen is a complex carbohydrate
• test for reducing sugars through benedicts test
• benedict's test turns blue when there are no reducing sugars present, green if trace amounts, orange if moderate amount, brick red if large amount
• procedure for benedicts test:

  1. place 2 cm3 of each food sample into a test tube
  2. add 2 cm3 of benedicts solution to the food sample
  3. shake the mixture and place the test tube in a boiling water bath for 2-3 minutes
  4. record the colour of the solution
• occurrence of the complex carbohydrates:

  starch-found in storage organs of plants, e.g. potato tubers and tapioca

  cellulose-present in cell walls of plants

  glycogen- stored in the liver of muscles of mammals
• the enzyme amylase digests starch to form the sugar maltose. maltose is then hydrolysed to glucose by the enzyme maltase
• functions of carbohydrates:

  -to provide energy for cell activities through respiration

  -to form supporting structure (e.g. cell walls in plants)

  -to be converted into other organic compounds such as amino acids and fats
• test for starch through iodine test
• procedures for iodine test:

  1. add a few drops of iodine solution to food sample
  2. record your observations
• fats are made up of carbon, hydrogen, oxygen
• fats are broken down into fatty acids and glycerol
• functions of fats:

  -source and long term storage of energy

  -insulation material that prevents excessive heat loss
• test for fats through ethanol emulsion test
• procedures for ethanol emulsion test:

  1. add 2 cm3 of ethanol to a drop of liquid sample in a test tube and shake the mixture thoroughly
  2. add 2 cm3 of water to the mixture and shake the mixture
  3. record your observation

  observation: the white emulsion indicates presence of fats
• proteins are made up of carbon, hydrogen, oxygen, nitrogen and sometimes sulfur
• proteins are digested into polypeptides which is then digested into amino acids
• test for proteins through biuret test
• procedures for biuret test:

  1. to 2 cm3 of liquid food sample add an equal volume of biuret solution
  2. shake well and allow mixture to stand for 5 minutes
  3. record your observation

  observation: purple colour indicates the presence of proteins