Carbohydrates

• Which molecule found in an organism is a monomer found in an enzyme's active site?

  Amino acid
• Which molecule found in an organism is a monomer of cellulose?

  Beta glucose
• Which molecule found in an organism is produced during photosynthesis and respiration?

  ATP
• Which molecule found in an organism forms a polymer that gives a positive result with a Biuret test?

  Amino acid
• Raffinose is a trisaccharide of three monosaccharides: galactose, glucose and fructose. The chemical formulae of these monosaccharides are:

  • galactose = C6H12O6

  • glucose = C6H12O6

  • fructose = C6H12O6

  Give the number of carbon atoms, hydrogen atoms and oxygen atoms in a molecule of raffinose.

  C = 18,

  H = 32,

  O = 16
• A biochemical test for reducing sugar produces a negative result with raffinose solution. Describe a biochemical test to show that raffinose solution contains a non-reducing sugar.

  1. Heat with acid and neutralise;

  2. Heat with Benedict's solution;

  3. Red precipitate
• A precipitate is produced in a positive result for reducing sugar in a Benedict's test. A precipitate is solid matter suspended in solution. A student carried out the Benedict's test. Suggest a method, other than using a colorimeter, that this student could use to measure the quantity of reducing sugar in a solution.

  1. Filter and dry the precipitate;

  2. Find mass
• What is a monomer?

  a smaller repeating unit from which larger polymers are made;
• Lactulose is a disaccharide formed from one molecule of galactose and one molecule of fructose. Other than both being disaccharides, give one similarity and one difference between the structures of lactulose and lactose.

  Similarity

  1. Both contain galactose

  Both contain a glycosidic bond;

  
  

  Difference

  2. Lactulose contains fructose, whereas lactose contains glucose
• Glycogen and cellulose are both carbohydrates. Describe the differences between the structure of a cellulose molecule and a glycogen molecule.

  1. Cellulose is made up of β-glucose monomers and glycogen is made up of α-glucose monomers;

  2. Cellulose molecule has straight chain and glycogen is branched;

  3. Cellulose molecule has straight chain and glycogen is coiled;

  4. glycogen has 1,4- and 1,6- glycosidic bonds and cellulose has only 1,4- glycosidic bonds;
• Starch is a carbohydrate often stored in plant cells. Describe and explain the features of starch that make it a good storage molecule

  1. Insoluble in water, so doesn't affect water potential;

  2. Branched and coiled , so makes molecule compact;

  3. Polymer of alpha glucose so provides glucose for respiration;

  4. Branched and more ends for enzyme action;

  5. Large molecule, so can't cross the cell membrane
• Which test would be used to show the presence of starch?

  Iodine test
• In mammals, in the early stages of pregnancy, a developing embryo exchanges substances with its mother via cells in the lining of the uterus. At this stage, there is a high concentration of glycogen in cells lining the uterus. Describe the structure of glycogen.

  Polysaccharide of alpha glucose joined by glycosidic bonds
• In mammals, in the early stages of pregnancy, a developing embryo exchanges substances with its mother via cells in the lining of the uterus. At this stage, there is a high concentration of glycogen in cells lining the uterus.

  During early pregnancy, the glycogen in the cells lining the uterus is an important energy source for the embryo.

  Suggest how glycogen acts as a source of energy. Do not include transport across membranes in your answer

  1. Hydrolysed to glucose;

  2. Glucose used in respiration;
• Name the monomers from which a maltose molecule is made.

  Glucose and glucose
• Name the type of chemical bond that joins the two monomers to form maltose.

  1,4 Glycosidic bond
• Starch molecules and cellulose molecules have different functions in plant cells. Each molecule is adapted for its function.

  Explain the ways in which starch molecules are adapted for their function in plant cells.

  1. Insoluble so it does not affect water potential;

  2. Helical so it is compact;

  3. Large molecule so it cannot leave cell.
• Starch molecules and cellulose molecules have different functions in plant cells. Each molecule is adapted for its function.

  Explain how cellulose molecules are adapted for their function in plant cells.

  1. Long and straight chains;

  2. Become linked together by many hydrogen bonds to form fibrils;

  3. Provide strength to cell wall.