4 - Biomolecules

• Large molecules made from smaller molecules

  • Starch from glucose
  • Glycogen from glucose
  • Cellulose from glucose
  • Proteins from amino acids
  • Fats and oils from fatty acids and glycerol
• Water is important as a solvent
• Structure of DNA


  • Two strands coiled together to form a double helix
  • Each strand contains chemicals called bases
  • Cross-links between the strands are formed by pairs of bases
  • The bases always pair up in the same way: A with T, and C with G
• Components of cells


  • 80% of water
  • Carbohydrates
  • Proteins
  • Fats
• Carbohydrates


  Made of carbon (C), hydrogen (H), oxygen (O)
• Basic unit of carbohydrates

  Glucose
• Forms of carbohydrates


  • Monosaccharide
  • Disaccharide
  • Polysaccharide
• Properties of carbohydrates


  • Soluble in water
  • Tastes sweet
• Properties of polysaccharides


  • Insoluble in water
  • Do not taste sweet
• Examples of monosaccharides

  • Glucose
  • Fructose
  • Galactose
• Examples of disaccharides


  • Sucrose
  • Maltose
  • Lactose
• Examples of polysaccharides

  • Cellulose
  • Starch
  • Glycogen
• All monosaccharides such as glucose are reducing sugars
• A disaccharide can be a reducing sugar or a non-reducing sugar
• Maltose and lactose are reducing sugars
• Glucose


  Release energy by respiration
• Animals store carbohydrates


  As glycogen
• Plants store carbohydrates

  As starch
• Plants transport carbohydrates


  As sucrose
• Testing for reducing sugars

  1. Use Benedict’s solution

  2. Heat the sample

  3. Observe color change
• Color changes of Benedict’s solution


  • Blue
  • Green
  • Yellow and orange
  • Brick red
• Food with no reducing sugars remains blue
• Testing for starch


  1. Use iodine solution

  2. Observe color change
• Color changes of iodine solution

  • Brown
  • Blue-black
• Food with starch turns blue-black
• Food with no starch remains brown
• All simple sugars, and some complex sugars such as maltose, are reducing sugars
• Testing for fats


  1. Use ethanol emulsion test

  2. Chop food

  3. Shake with ethanol

  4. Pour into water

  5. Observe
• Observation for presence of fats

  • Clear to white emulsion
• Food remains clear if fats are absent
• Fats


  Made of carbon, hydrogen, and oxygen
• Basic unit of fats

  1 glycerol + 3 fatty acids
• Properties of fats


  • Insoluble in water
  • At room temperature, fats are called oils
• Cells only use fats when all available carbohydrates have been used
• Adipose tissue


  Fat tissues that insulate the body
• Examples of plants storing oils

  • Peanut
  • Coconut
  • Castor oil
• The oils provide a good store of energy for germination
• Fats are used for energy storage in mammals
• Fats are used for energy storage in plants
• Fats help in making cell membranes