Carbohydrates

• Fructose + Glucose -> Sucrose
• Glucose + Glucose -> Maltose
• Glucose + Galactose -> lactose
• What is the test for reducing sugars?

  Benedict’s test

  2cm3 of food sample

  add Benedict’s reagent

  heat in boiling water for 5 mins

  if positive, turns brick red
• What is the test for non-reducing sugars?

  Repeat Benedict’s test

  If no result add 2cm3 of food sample to hydrocholoric acid

  Place in a boiling water bath for 5 mins

  This will hydrolyse the disaccharides into their monosaccharides

  Slowly add sodium hydrogencarbonate to neutralise the HCl

  Repeat Benedict’s test

  If positive solution turns orange-brown
• What is glycogen made out of?

  Alpha glucose
• What are the two isomers of glucose?

  Alpha glucose and beta glucose
• What bonds are in glycogen?

  Glycosidic
• How are the bonds formed in glycogen?

  Condensation reactions
• What is the structure of glycogen?

  Short chains

  Highly branched
• What is glycogen used for?

  Energy storage in animals
• Why is glycogen suitable for energy storage?

  Insoluble -> won’t diffuse out of cells

  Highly branched -> more ends to be acted on by enzymes

  Rapidly broken down into glucose
• What is starch made of?

  Alpha glucose
• What is the structure of starch?

  Chains branched (amylose) or unbranched (amylopectin)

  Unbranched chains are wound into tight coils that make the molecule compact
• What does starch do?

  Energy storage in plants
• How is starch suitable for energy storage?

  • Large and insoluble -> won’t diffuse out of cells
  • Compact -> a lot fits in a small space
  • When hydrolysed forms alpha glucose
• What is the test for starch?

  Add iodine to food sample, if positive turns blue-black
• What makes up cellulose?

  Beta glucose molecules, rotated 180° to allow hydrogen bonds between OH groups
• How are cellulose molecules grouped?

  To form microfibrils, which are arranged to form fibrils
• What is cellulose used for?

  Providing rigidity to the cell wall of plants
• How is cellulose good for cell walls?

  • Straight unbranched chains
  • Chains are cross-linked by hydrogen bonds
  • Fibrils provide strength