U-4 biological molecules

• Carbohydrates

  Molecules made from three elements: carbon, hydrogen, oxygen
• Examples of carbohydrates

  • Starch
  • Cellulose
  • Glycogen
  • Glucose
  • Maltose
• Carbohydrate molecule


  • Contains 6 carbon atoms in a hexagon shape
• Glucose

  Dissolves in blood plasma, which delivers it to every cell
• Glucose conversion

  Glucose converted to glycogen in liver and muscle
• Cellulose

  Used for making plant cell walls
• Monosaccharides

  One basic molecule
• Disaccharides

  Two monosaccharides joined together
• Monosaccharides in food products

  • Fructose
  • Glucose
  • Galactose
  • Ribose
• Disaccharides in food

  • Sucrose
  • Maltose
  • Lactose
• Sucrose

  Glucose + Fructose
• Maltose


  Glucose + Glucose
• Lactose

  Glucose + Galactose
• Starch detection

  Add iodine solution
• Sugar detection

  Add Benedict's solution, heat
• Starch and cellulose


  Both made of glucose molecules, but starch coils into a spiral shape while cellulose lies straight
• Starch breakdown

  Broken down by enzyme amylase (in saliva, pancreas)
• Proteins

  Contain four elements: carbon, hydrogen, oxygen and nitrogen
• Types of proteins

  • Antibodies
  • Enzymes
  • Hormones
  • Structural proteins (collagen)
  • Storage proteins (Ferritin)
  • Transport proteins (haemoglobin, carrier proteins)
• Biuret reagent

  Used to test for proteins (turns blue to violet)
• Nitrogen is the element found in proteins but not in carbohydrates and fats
• Vitamin C test


  Use DCPIP reagent (turns blue to colourless)
• Keratin is not soluble in water as it is found in hair and nails
• Lipids


  Also known as fats and oils, contain three elements: carbon, hydrogen, oxygen
• Fat breakdown

  Broken down into fatty acids and glycerol by lipase enzyme
• Lipids


  • Used to make cell membranes
  • Stored as an energy source
  • Do not dissolve in water but dissolve in ethanol
  • Provide heat insulation
• DNA


  Carries the genetic code that instructs cells to make proteins
• DNA structure


  • Double helix shape
  • Made of nucleotides containing a sugar, phosphate and one of four bases: A, C, G, T
  • Base pairs are complementary (A-T, C-G)