Unit 1 Biological Molecules

Question 1

What is hydrolysis?

Answer 1

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

Question 2

What is a condensation reaction?

Answer 2

1. Creates a chemical bond
2. Removing a molecule of water

Question 3

Glycogen - Glycogen Structure (3)

Answer 3

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

Question 4

Glycogen - Glycogen compared

with cellulose (4)

Answer 4

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

Question 5

Glycogen - Glycogen structure

related to function (5)

Answer 5

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 6

Starch – Relate 3 properties to its

function (6)

Answer 6

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

Question 7

Test for reducing sugar

Answer 7

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

Question 8

Test for a non reducing sugar

Answer 8

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

Question 9

Test for starch

Answer 9

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

Question 10

How are triglycerides formed

Answer 10

1.      One glycerol and three fatty acids;

2.      Condensation(reactions) and removal of three molecules of water;

3.      Ester bond(s) (formed);

Question 11

Phospholipids compared with

Triglycerides (8)

Answer 11

1. Both contain ester bonds (between glycerol and fatty acid);
2. Both contain glycerol;
3. Fatty acids on both may be saturated or unsaturated;
4. Both are insoluble in water;
5. Both contain C, H and O but phospholipids also contain P;
6. Triglyceride has three fatty acids and phospholipid has two fatty acids plus phosphate group;
7. Triglycerides are hydrophobic/non-polar and phospholipids have hydrophilic/polar and hydrophobic/polar

region;

8. Phospholipids form monolayer (on surface)/micelle/bilayer (in water) but triglycerides don’t;

Question 12

Describe how an ester bond is formed in a phospholipid molecule.

Answer 12

1. Condensation reaction
2. Between glycerol and fatty acid

Question 13

Test for a lipid

Answer 13

1.      (Mix / shake sample) with ethanol, then water;

Sequence is important

2.      White / milky (emulsion);

Question 14

ATP – Uses and properties as an energy source (5)

Answer 14

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 15

ATP – Structure compared with DNA nucleotide (3)

Answer 15

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 16

Water – Properties that make water important for organisms (6)

Answer 16

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