Biological Molecules Recall Q

Question 1

Describe the chemical reactions involved in the conversion of polymers to monomers and monomers to polymers. Give two named examples of polymers and their associated monomers to illustrate your answer. (5 marks)

Answer 1

1. A condensation reaction joins monomers together and forms a (chemical) bond and releases water;
2. A hydrolysis reaction breaks a (chemical) bond between monomers and uses water;
3. A suitable example of polymers and the monomers from which they are made;
4. A second suitable example of polymers and the monomers from which they are made;
5. Reference to a correct bond within a named polymer;

Question 2

Describe how the structures of starch and cellulose molecules are related to their functions. (5 marks)

Answer 2

1. Helical/spiral shape so compact;
2. Molecule is insoluble so osmotically inactive (does not affect water potential)
3. Branched so glucose is easily accessible by enzymes to break down for respiration;
4. Large molecule so cannot leave cell/cross cell-surface membrane
   Cellulose (max 3)
5. Long, straight & unbranched chains of β glucose;
6. Joined by hydrogen bonding, to form (micro/macro) fibrils
7. These provide rigidity/strength;

Question 3

Describe the structure of a cellulose molecule and explain how cellulose is adapted for its function in cells (6 marks)

Answer 3

1. made from β-glucose;
2. joined by condensation to form glycosidic bond; 3. 1 : 4 link described;
3. “flipping over” of alternate molecules;
4. hydrogen bonds linking long straight chains;
5. cellulose makes cell walls strong;
6. can resist turgor pressure/osmotic pressure;
7. bond difficult to break;
8. resists action of enzymes

Question 4

Describe the structure of proteins (5 marks)

Answer 4

1. polymer of amino acids
2. Joined by peptide bonds;
3. That are formed by condensation;
4. Primary structure is the order of amino acids;
5. Secondary structure is folding of polypeptide chain due to hydrogen bonding;
6. Tertiary structure is 3-D folding due to hydrogen bonding and ionic / disulfide
   bonds;
7. Quaternary structure is two or more polypeptide chains

Question 5

ATP is useful in many biological processes. Explain why (4 marks)

Answer 5

1. Releases energy in small & easily
   manageable amounts;
2. Broken down in a one step reaction which
   makes sure energy is available
   rapidly;
   3.Phosphorylates substances to make them
   more reactive
   4.Reformed/made again rapidly

Question 6

Describe the biochemical tests you would use to confirm the presence of lipid, non-reducing
sugar and amylase in a sample (5 marks)

Answer 6

1. Add ethanol/alcohol and shake/mix then pour
   into/add water;
2. White/milky emulsion
   Non-reducing sugar
3. Do Benedict’s test and stays blue/negative;
4. Boil with acid then neutralise with alkali;
5. Heat with Benedict’s and becomes red/orange
   (precipitate);
   Amylase
6. Add biuret (reagent) and becomes
   purple/violet/mauve/lilac;
7. Add starch, (leave for a time), test for reducing
   sugar/absence of starch;

Question 7

Haemoglobins are chemically similar molecules found in many different species. Differences
in the primary structure of haemoglobin molecules can provide evidence of phylogenetic
(evolutionary) relationships between species. Explain how. (5 marks)

Answer 7

1. Mutations change base / nucleotide
   (sequence);
2. (Causing) change in amino acid sequence;
3. Mutations build up over time;
4. More mutations / more differences (in amino
   acid/ base / nucleotide sequence / primary
   structure) between distantly related species;
5. Distantly related species have earlier common
   ancestor;

Question 8

Describe the roles of iron ions, sodium ions and phosphate ions in cells (5 marks)

Answer 8

1. Haemoglobin binds/associates with oxygen
   Sodium ions
2. Co-transport of glucose/amino acids (into
   cells);
3. (Because) sodium moved out by active
   transport/Na – K pump;
4. Creates a sodium concentration/diffusion
   gradient;
5. Affects osmosis/water potential;
   Phosphate ions
6. Affects osmosis/water potential;
7. Joins nucleotides/in phosphodiester bond/in
   backbone of DNA/RNA/in nucleotides;
8. Used in/to produce ATP;
9. Phosphorylates other compounds (usually)
   making them more reactive;
10. Hydrophilic/water soluble part of
    phospholipid bilayer/membrane;

Question 9

Explain five properties that make water important for organisms (5 marks)

Answer 9

1. A metabolite in condensation/hydrolysis/
   photosynthesis/respiration;
2. A solvent so (metabolic) reactions can occur
3. High heat capacity so buffers changes in
   temperature;
4. Large latent heat of vaporisation so provides a
   cooling effect (through evaporation);
5. Cohesion (between water molecules) so
   supports columns of water (in plants);
6. Cohesion (between water molecules) so
   produces surface tension supporting (small)
   organisms;

Question 10

Mucus also contains glycoproteins. One of these glycoproteins is a polypeptide with the sugar,
lactose, attached. Describe how lactose is formed and where in the cell it would be attached to a polypeptide to form a glycoprotein. (4 marks)

Answer 10

1. Glucoseandgalactose;
   2.Joined by condensation (reaction);
   3.Joined by glycosidic bond;
   4.Added to polypeptide in Golgi (apparatus)