3.1.2 Carbohydrates

• Main function - provide energy through aerobic respiration in the mitochondria
• Alpha glucose

  
• Beta glucose

  
• Monosaccharides - glucose, fructose, galactose
• Disaccharides - two monosaccharides bonded together with a glyosidic bond. They are digested as they are too large to be absorbed into the blood. In a lab the bond can be broken by boiling with acid.

  • Maltose - alpha & alpha glucose
  • Sucrose - alpha glucose & fructose (non-reducing sugar)
  • Lactose - alpha glucose & galactose
• Starch

  • Polymer
  • insoluble in water - water cannot enter the cell via osmosis
  • Store of alpha glucose in plant cells
  • Storage molecule - coiled, more compact = less space required
  • Large - cannot diffuse across the c.s.m
• Glycogen

  • Polymer
  • Insoluble in water - prevents osmosis
  • Store of alpha glucose in animal cell (+prokaryotic + fungi)
  • Highly branched - more compact = more ends so that glucose can be released quicker (hydrolyse)
• Cellulose

  • Polymer of beta glucose
  • Makes a strong cell wall to support the cell and prevent cell lysis (bursting) - the cell is fully permeable
  • Long, straight chain
  • high tensile strength
  • Every alternate glucose is flipped 180 degrees
• Test for reducing sugars 


  Add test solution and an equal amount of benedicts solution

  Heat for 3 minutes

  Positive result (from blue) forms a brick red precipitate
• Test for starch

  Add a few drops of iodine in potassium iodide

  Positive result is a colour change to blue/black
• Test for non-reducing sugar

  Try the reducing sugar test

  if negative -

  add test solution and hydrochloric acid

  boil

  allow to cool then add an alkali

  Benedicts test - brick red precipitate
• Describe a method to make a biochemical test fully quantitative

  Vary concentration of test solution

  Use a colourimeter to measure absorbance of light

  Filter and dry precipitate and then measure mass