Biological molecules

• Carbohydrates


  • Monosaccharides
  • Disaccharides
  • Polysaccharides
• Monosaccharides


  Simple sugars
• Monosaccharides

  • glucose (grape sugar)
  • fructose (fruit sugar)
  • galactose (milk sugar)
• Disaccharides


  Double sugars, formed by condensation reaction between 2 simple sugars
• Disaccharides


  • maltose (malt sugar in barley)
  • sucrose (cane sugar)
  • lactose (milk sugar)
• Polysaccharides


  Multiple sugars, formed by condensation reaction of many simple sugars, not sweet and insoluble in water
• Polysaccharides


  • starch
  • glycogen
  • cellulose
• Carbohydrates


  • Organic compounds containing carbon, hydrogen and oxygen
  • General formula = Cx(H2O)y
• Benedict's test for reducing sugars


  1. Add Benedict's solution to food sample

  2. Boil in water bath at 80-100°C for 5 minutes

  3. Colour changes from blue to green to yellow to orange to bright red, indicating presence of reducing sugars
• Iodine test for starch

  1. Add iodine solution to sample

  2. Blue-black colour indicates presence of starch

  3. Yellowish-brown colour indicates absence of starch
• Lipids (Fats)


  • Saturated fats (unhealthy)
  • Unsaturated fats (healthy)
• Saturated fats


  Cannot take in any more 4-atoms, straight chained, contain only C-C single bonds, have higher melting point
• Unsaturated fats


  Can take in 1 or more pairs of 4-atoms, bent at some places, contain 1 or more C=C double bonds, have lower melting point
• Edible products rich in fat

  • cooking oil
  • margarine
  • dairy products
  • snack food
  • mayonnaise
• Lipids


  Organic compounds containing carbon, hydrogen and oxygen<|>Energy providing foods<|>Solid at room temperature (20-25°C) are called fats, liquid at room temperature (20-25°C) are called oils<|>Formed by condensation reaction between fatty acids and glycerol
• Grease-spot test for fats


  1. Put a drop of oil on filter paper and hold to light

  2. A translucent spot is seen
• Ethanol emulsion test for fats

  1. Add ethanol to oil, shake to dissolve

  2. Add water and shake

  3. A cloudy white emulsion is formed, indicating presence of fats
• Proteins


  • Amino acids
  • Dipeptides
  • Polypeptides
  • Protein molecules
• Proteins


  Organic compounds containing carbon, hydrogen, oxygen and nitrogen<|>Made up of amino acids
• Properties of proteins


  • Easily denatured by high temperature or extreme pH
  • Insoluble in water
  • Very large, cannot pass across cell membrane or be absorbed into body, have to be broken down by enzymes during digestion
• Biuret test for proteins

  1. Add sodium hydroxide and copper sulphate to food sample

  2. Purple colour indicates presence of proteins, blue colour indicates absence
• DNA (deoxyribonucleic acid)


  Material that makes up genes and chromosomes<|>Made up of nucleotides containing pentose sugar, nitrogen-containing base, and phosphate group
• Structure of DNA

  1. Many nucleotides join to form polynucleotide chains

  2. Two polynucleotide chains twisted around each other to form double helix