KEY BIOLOGICAL MOLECULES

Question 1

describe the chemical reactions involved in the conversion of polymers to monomers and monomers to polymers, give two named examples in your answer (5)

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)

Answer 2

Starch (max 3)

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 (6)

Answer 3

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

Question 4

describe the structure of proteins

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)

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 lipids, non reducing sugars and amylase in a sample (5)

Answer 6

Lipid
1. Add ethanol/alcohol then add water and shake/mix
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 phylogenic (evolutionary) relationships between species. explain how (5)

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. Closely related species have recent common ancestor;

Question 8

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

Answer 8

Iron ions
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)

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)

Answer 10

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