1) Biological Molecules

Question 1

What is hydrolysis

Answer 1

1. Breaks a chemical bonds between two molecules;
2. Using water;

Question 2

Structure of glycogen

Answer 2

1. Polysaccharide of α-glucose;
2. (Joined by) glycosidic bonds;
3. Branched structure;

Question 3

Compare glycogen molecule with cellulose

Answer 3

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 hxas only 1,4- glycosidic bonds

Question 4

Structure of glycogen related to its function

Answer 4

1) Insoluble (in water), so doesn’t affect water potential;

2) Branched / coiled / (α-)helix, so makes molecule compact;

3) Polymer of (α-)glucose so provides glucose for respiration;

4) Branched / more ends for fast breakdown / enzyme action;

5) Large (molecule), so can’t cross the cell membrane

Question 5

Structure of starch related to its function

Answer 5

1. Insoluble - Don’t affect water potential;
2. Helical - Compact;
3. Large molecule - Cannot leave cell;

Question 6

Phospholipids compared with
Triglycerides

Answer 6

• Both contain ester bonds (between glycerol and fatty acid);
• Both contain glycerol;
• Fatty acids on both may be saturated or unsaturated;
• Both are insoluble in water;
• Both contain C, H and O but phospholipids also contain P;
• Triglyceride has three fatty acids and phospholipid has two fatty acids plus phosphate group;
• Triglycerides are hydrophobic/non-polar and phospholipids have hydrophilic/polar and hydrophobic/polar
  region;
• Phospholipids form monolayer (on surface)/micelle/bilayer (in water) but triglycerides don’t;

Question 7

Structure of protein

Answer 7

1. Polymer of amino acids;
2. Joined by peptide bonds;
3. Formed by condensation;
4. Primary structure is 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;
6. Quaternary structure is two or more polypeptide chains;

Question 8

Induced fit model of enzyme

Answer 8

1. (before reaction) active site not complementary to/does not fit substrate;
2. Shape of active site changes as substrate binds/as enzyme-substrate complex forms;
3. Stressing/distorting/bending bonds (in substrate leading to reaction);

Question 9

Increased temperature and reaction rate - enzymes

Answer 9

1. particles have more kinetic energy
2. therefore they move more
3. so there are more collisions between substrates and active sites
4. so more ES complexes form

Question 10

Denaturation- enzymes

Answer 10

1. Heat above the optimum breaks hydrogen bonds
2. this causes the tertiary structure to unfold
3. so the active site changes shape
4. substrate can no longer bind to the active site, as it’s no longer complementary
5. so fewer ES complexes form

Question 11

Effect of Changes in pH on enzymes

Answer 11

1. Ionic bonds holding tertiary structure break
2. active site distorts and substrate no longer binds to active site
3. charges on amino acids in active site affected
4. fewer ES complexes form

Question 12

Concentration of
Substrate - enzymes

Answer 12

1. (Rate of) increase in concentration of product slows as substrate is used up OR High initial rate as plenty of substrate/more E-S complexes;
2. No increase after 25 minutes/at end/levels off because no substrate left;

Question 13

Describe and explain
the temperature graph of enzyme
rate

Answer 13

1. Initial rate of reaction faster at 37 °C (than 25 °C);
2. Because more kinetic energy;
3. So more E–S collisions/more E–S complexes formed;
4. Graph reaches plateau /levels off at 37 °C;
5. Because all substrate used up;

Question 14

Comparison of
Competitive and Non Competitive
Inhibition

Answer 14

1. Competitive inhibitor binds to active sites of enzyme but non-competitive inhibitor binds at allosteric site/away from active site;
2. (Binding of) competitive inhibitor does not cause change in shape of active site but (binding of) non-competitive does (cause change in size of active site);
3. So with competitive inhibitor, at high substrate concentrations (active) enzyme still available but with non- competitive inhibitor (active) enzymes no longer available;
4. At higher substrate concentrations likelihood of enzyme-substrate collisions increases with competitive inhibitor
   but this is not possible with non-competitive inhibitor;

Question 15

Effect of temperature linked to plant growth - enzymes

Answer 15

(As temperature increases,)

1. Enzyme activity reduced/(some) enzymes denatured;
2. Less photosynthesis, so fewer sugars formed (plants only);
3. Less (complex) biological molecules/organic substances made (that add to mass);
4. Less respiration;
5. Less energy/ATP for growth;
6. Less energy for named function associated with growth (eg mitosis)

Question 16

What is DNA replication

Answer 16

1.Helicase unzips DNA double helix
2. by breaking hydrogen bonds
3. free DNA nucleotides in the nucleus complementary base pair OR A to T and C to G;
4. with exposed bases on both strands
5. hydrogen bonds between complementary base pairs reform
6. both strands act as a template
7. DNA polymerase (causes);
Nucleotides to join together (to form new strand)/phosphodiester bonds to form;

Question 17

DNA Semi-Conservative Replication

Answer 17

1. Idea of both original strands being copied/both are template strands;
2. Each new DNA molecule consists of one original and one new strand of DNA;

Question 18

Uses and properties of ATP as an
energy source

Answer 18

1. Releases relatively small amount of energy / little energy lost as heat;
2. Releases energy instantaneously;
3. Phosphorylates other compounds, making them more reactive;
4. Can be rapidly re-synthesised;
5. Does not leave cells;

Question 19

ATP Structure compared with
DNA nucleotide

Answer 19

1. ATP has ribose and DNA has deoxyribose;
2. ATP has 3 phosphates and DNA nucleotide has one phosphate;
3. Base is always adenine in ATP and bases vary in DNA nucleotide (A,C,G or T);

Question 20

Properties that make water
important for organisms

Answer 20

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 organisms;

Question 21

Test for reducing sugar

Answer 21

1. Heat with Benedict’s reagent (1);
2. colour change from blue to brick-red

Question 22

Test for non reducing sugar

Answer 22

1.Heat with Benedict’s reagent and no colour change (1);
2. boil with dilute HCl and then neutralise with NaHCO3 (1);
3. re- heat with Benedict’s reagent and colour change from blue to brick-red (1)

Question 23

Test for starch

Answer 23

• Add iodine in potassium iodide solution (1);
• colour change from brown to blue-black (1)

Question 24

Test for protein

Answer 24

• Add Biuret reagent to the sample (1);
• colour change to lilac (1) (or lilac band appears)

Question 25

Emulsion test - lipid

Answer 25

- Add ethanol and shake (1); - add water and goes milky (1)