Biological molecules

• Molecules in living organisms

  • Carbohydrates
  • Proteins
  • Lipids
• These molecules all contain carbon and are described as organic molecules
• Carbohydrates

  • Long chains of simple sugars
  • Glucose is a simple sugar (monosaccharide)
  • Maltose is formed when 2 glucose molecules join (disaccharide)
  • Starch, glycogen or cellulose can form when lots of glucose molecules join (polysaccharide)
• Fats (lipids)

  • Most fats in the body are made up of triglycerides
  • Triglycerides have 1 glycerol molecule chemically bonded to 3 fatty acid chains
  • Lipids are divided into fats (solids at room temperature) and oils (liquids at room temperature)
• Proteins


  • Long chains of amino acids
  • There are about 20 different amino acids
  • Amino acids can be arranged in any order, resulting in hundreds of thousands of different proteins
  • Even a small difference in the order of amino acids results in a different protein being formed
• Food Tests

  1. Test for glucose (Benedict's solution)

  2. Test for starch (iodine)

  3. Test for protein (Biuret solution)

  4. Test for lipids (ethanol)

  5. Test for vitamin C (DCPIP)
• When describing food tests, give the starting colour of the solution and the colour it changes to for a positive result
• DNA


  • DNA, or deoxyribonucleic acid, is the molecule that contains the instructions for the growth and development of all organisms
  • DNA consists of two strands wound around each other in a double helix
  • The individual units of DNA are called nucleotides
  • Nucleotides contain a phosphate, deoxyribose sugar, and one of four bases: Adenine (A), Cytosine (C), Thymine (T), or Guanine (G)
  • The bases on each strand pair up with each other, holding the two strands of DNA in the double helix
  • Adenine always pairs with Thymine (A-T), and Cytosine always pairs with Guanine (C-G)
  • The phosphate and sugar section of the nucleotides form the 'backbone' of the DNA strand, and the base pairs of each strand connect to form the 'rungs' of the ladder
• The DNA helix is made from two strands of DNA held together by hydrogen bonds
• The sequence of bases holds the code for the formation of proteins