exam questions

• compare and contrast the structures of saturated and unsaturated fatty acids (4)

  • (They both have) hydrocarbon tails
  • (They both have) a (carboxylic) acid / -COOH group at one end
  • Saturated has more hydrogen/H atoms / only C-C single bonds
  • Unsaturated has C=C double bonds
  • Unsaturated can have kinked chains / saturated has straight chains
• compare the structure of alpha and beta glucose

  -        Both hexose sugars / contain 6 carbon atoms

  -        Both have a ring structure

  -        Carbon 6 sticks out above/below the ring

   

  -        The location/orientation of the -H and -OH group on carbon 1

  -        Alpha glucose has the H above carbon 1 and the OH group below

  -        Beta glucose has the H below carbon 1 and the OH group above
• state 2 features of glycosidic bonds that form between 2 monosaccharides in a condensation reaction

  -       A glycosidic bond is) formed from 2 -OH groups (on separate monosaccharides)

  -       Strong, covalent bond

  -       Act as a bridge via one oxygen atom / are formed -O- etc

  -       Links either C1 to C6 or C1 to C4
• explain the name of the type of reaction that forms the carbohydrates in part a from their monomers (2)

  -       A condensation reaction where a water molecule is released from the reaction as a by-product.
•  state 2 features of starch and explain how these features allow starch to act as a storage substance(4 marks)

  • Feature 1: Branched chains
  • Easy to remove glucose molecules/ fast breakdown/easily hydrolysed
  • Feature 2: Insoluble
  • no osmotic effect
  • Feature 3: Coiled/helical/spiral structure
  • Can fit many molecules into a small area/compact
  • Feature 4: Large molecule OR long chain
  • Contains many glucoses molecules

   

   
• explain how the structure of glycogen allows it to be an energy store(3)

  • polymer of glucose
  • to provide glucose for respiration
  • branched(1,6 glycosidic bonds)/ many terminal ends for rapid hydrolysis
  • compact to allow large amount of glucose/energy to be stored in a small space
• Describe the reaction that joins two α-glucose molecules to form a disaccharide(2)

  • condensation reaction
  • producing a H20 molecule
  • forming glycosidic bonds
• give one structural difference between amylose and amylopectin(1)

  • amylose is unbranched( only 1,4 glycosidic bonds)
  • amylopectin is branched(1,4 and 1,6 glycosidic bonds)
• Explain how the structures of amylopectin and glycogen make them suitable for storing energy(3)

  • branched thus can be rapidly hydrolysed(to release glucose)
  • compact so more energy/glucose can be stored
  • insoluble thus does not affect osmosis
  • molecules too large to diffuse across cell surface membrane
• Compare and contrast the structure of a disaccharide with glycogen(4)

  • both contain carbon, hydrogen and oxygen
  • both contain glycosidic bonds
  • both contain glucose
  • glycogen contains 1,4 and 1,6 glycosidic bonds whereas disacchariodes only one type of glycosidic bond
  • glycogen only contains glucose whereas disaccharides can contain glucose and other monosaccharides
• describe the structure of an unbranched polysaccharide

  • made up of many monosaccharide components
  • joined together by condensation reactions/glycosidic bonds
  • only 1,4 glycosidic bonds present, no 1,6 bonds
• describe how the structure of glycogen is related to its function as a storage molecule(2)

  • branched molecule for more rapid hydrolysis
  • compact so more can be stored