Monomers and polymers + carbohydrates

• Define monomer. Give some examples

  Smaller units that join together to form larger molecules

  • monosaccharides (glucose, fructose, galactose)
  • amino acids
  • nucleotides
• Define polymer. Give some examples

  Molecules formed when many monomers join together

  • polysaccharides
  • proteins
  • DNA/RNA
• What happens in a condensation reaction?

  A chemical bond forms between 2 molecules & a molecule of water is produced
• What happens in a hydrolysis reaction?

  A water molecule is used to break a chemical bond between 2 molecules
• Name the 3 hexose monosaccharides

  .

  • glucose
  • fructose
  • galactose

  all have the molecular formula C6H12O6
• Name the type of bond formed when monosaccharides react

  glycosidic bond

  • 2 monomers = 1 chemical bond = disaccharide
  • multiple monomers = many chemical bonds = polysaccharide
• Name 3 disaccharides, describe how they form

  Condensation reaction forms glycosidic bond between 2 monosaccharides

  • maltose: glucose + glucose
  • sucrose: glucose + fructose
  • Lactose: glucose + galactose
• Structure of alpha-glucose

  
• Structure of beta-glucose

  
• Describe the structure and functions of starch

  Main storage polymer of alpha-glucose in animal cells (but also found in plant cells)

  • glycosidic bonds
  • branched = many terminal ends for hydrolysis
  • insoluble = no osmotic effect & does not diffuse out of cells
  • compact
• Describe the structure and function of cellulose

  Polymer of beta-glucose gives rigidity to plant cell walls (prevents bursting under turgor pressure, holds stem up)

  • glycosidic bonds
  • straight-chain, unbranched molecule
  • alternate glucose molecules are rotated 180 degrees
  • H-bond crosslinks between parallel strands form microfibrils = high tensile strength
• Describe Benedicts test for reducing sugars

  .

  1. add an equal volume of Benedicts reagent to a sample
  2. heat the micture in an electric water bath at 100 degrees for 5 minutes
  3. positive result: colour change from blue to orange & brick red precipitate forms
• Describe the Benedicts test for non-reducing sugars

  .

  1. negative result: benedicts reagent remains blue
  2. hydrolyse non-reducing sugars e.g sucrose into their monomers by adding 1cm3 of HCL. Heat in a boiling water bath for 5 mins
  3. neutralise the mixture using sodium carbonate solution
  4. proceed with the Benedicts test as usual
• Describe the test for starch

  .

  1. Add iodine solution
  2. positive result: colour change from orange to blue black
• Outline how colorimetry could be used to give qualitative results for the presence of sugars and starch

  .

  1. make standard solutions with known concentrations. Record absorbance or % of transmission values
  2. plot calibration curve
  3. record absorbance or % transmission values of unknown samples. Use calibration curve to read off concentration