Carbohydrates

• Monomers


  Smaller units from which larger molecules are made
• Polymers 


  molecules made from a large number of monomers joined together
• Examples of Monomers (3)

  • Amino Acids
  • Nucleotides
  • Monosaccharides
• Condensation Reaction 


  joins two molecules together with the formation of a chemical bond and involves the elimination of a molecule of water
• Hydrolysis Reaction


  breaks a chemical bond between two molecules and involves the use of a water molecule
• Monosaccharides 


  monomers from which larger carbohydrates are made
• Examples of Monosaccharides (3)


  Glucose

  Galactose

  Fructose
• A condensation reaction between two monosaccharides forms a glycosidic bond
• Disaccharides are formed by the condensation of two monosaccharides
• maltose is a disaccharide formed by condensation of two glucose molecules
• sucrose is a disaccharide formed by condensation of a glucose molecule and a fructose molecule
• lactose is a disaccharide formed by condensation of a glucose molecule and a galactose molecule.
• Glucose has two isomers, α-glucose and β-glucose
• Polysaccharides are formed by the condensation of many glucose units
• Glycogen and starch are formed by the condensation of α - glucose.
• Cellulose is formed by the condensation of β-glucose
• Starch Structure

  • helical shape so it is compact
  • insoluble so it is does not affect water potential
  • branched so glucose is released easily for respiration
  • large so it cannot leave the cell.
• Cellulose Structure

  • long, unbranched, straight chains of β glucose joined with beta-1,4-glycosidic bond
  • weak hydrogen bonds between the chains of beta-glucose.
  • form (micro/macro)fibrils
  • Provides rigidity/strength
• Glycogen Structure

  • Helical so compact
  • polymer of glucose so easily hydrolysed
  • branched so more ends for faster hydrolysis
  • made of glucose so provides respiratory substrate
  • insoluble so does not affect water potential.
• Which glucose isomer has compounds (OH & H ) of the same side?


  Alpha glucose
• Which glucose isomer has compounds (OH & H ) of the opposite side?


  Beta glucose
• A long, straight chain polysaccharide is the result of beta glucose and beta-1,4-bonds.
• Branched chains are formed from alpha-1,6-glycosidic bonds.
• Reducing sugar test

  1. grind sample in water
  2. add the same volume of Benedict's reagent
  3. heat in water bath for 5 mins
  4. Blue to orange/ brick-red
• all monosaccharides can be detected using Benedict’s reagent and some polysaccharides are reducing sugars
• Non- reducing sugars test

  1. Same steps for reducing sugar but will stay blue
  2. Add acid
  3. Boil for 5 mins
  4. neutralise with alkali
  5. heat with benedicts
  6. blue to red/orange
• Test for starch

  1. Add a food sample to a test tube
  2. Add iodine solution to the tube shake or stir the mixture
  3. shake or stir the mixture
  4. Brown to blue- black