BIOLOGICAL MOLECULES

Question 1

What are polymers? + examples.

Answer 1

• Large, complex molecules composed of long chains of monomers joined together.
• Lipids, proteins, DNA, carbohydrates.

Question 2

What are monomers?

Answer 2

• Small, basic molecular units.

Question 3

Describe lipids.

Answer 3

• Fats (solids) or oils (liquid).
• Plants and animals.
• Carbon, hydrogen and oxygen.
• Large molecules.

Question 4

Triglycerides structure.

Answer 4

• One glycerol + 3 fatty acids.
• Synthesised by a formation of ester bonds- concentration reaction (interaction of hydroxyl groups of fatty acids and glycerol interact and form a water molecule).
• Unsaturated = double carbon bonds. - Cause kink. - Molecules can’t lie packed together. - Liquids.
• Saturated = single carbon bonds.

Question 5

Triglyceride function.

Answer 5

• Insoluble. - Fatty acid tails face inwards (hydrophilic), shielding from water, no water enters by osmosis, bundle as water droplets.
• Energy storage molecules. - Long hydrocarbon tails of fatty acids contain lots of chemical energy therefore lots of energy released when broken down.
• Energy and carbon stores (bacteria).

Question 6

Saturated fatty acids.

Answer 6

• No double bonds.
• Saturated with hydrogen.

Question 7

Unsaturated fatty acids.

Answer 7

• Atleast one double carbon bond.
• Causes a kink in the chain so can’t pack closely together.
• Liquid at room temp (oils).
• 1 double = monounsaturated.
• 1+ double = polyunsaturated.
• unsaturated triglycerides = healthier.

Question 8

Phospholipids structure.

Answer 8

• Charged phosphate group (hydrophilic), glycerol molecule and 2 fatty acid tails (hydrophobic).
• Allow lipid soluble and small molecules through.

Question 9

Phospholipid function.

Answer 9

• Cell membranes. - Phospholipid bilayer. - Hydrophilic head (facing out) and hydrophobic tails (facing inwards) forming double layer. - Allows lipid soluble and small molecules to enter and leave the cell. - Acts as a barrier.
• Form a layer on the surface of water (head in water, tails out) [surfactant / surface active agents].

Question 10

Cholesterol structure.

Answer 10

• Small size and flattened shape.
• Fits between phospholipid molecules in membrane.
• Bind to hydrophobic tails causing them to pack closely.

Question 11

Cholesterol function.

Answer 11

• Help to strengthen membrane.
• Make membrane less fluid and more rigid.

Question 12

Sterol structure.

Answer 12

• Steroid alcohols.
• Complex alcohol molecules based on carbon 4 ring structure with a hydroxyl (OH) group on one end.
• Hydroxyl group is polar and hydrophilic, rest of molecule is hydrophobic.

Question 13

Roles of lipids.

Answer 13

• Membrane formation.
• Hormone production.
• Electrical insulation.
• Waterproofing.
• Thermal insulation.
• Buoyancy for aquatic animals such as whales .

Question 14

Testing for lipids.

Answer 14

• Ethanol.
• Milky = Lipid present.

Question 15

Inorganic cations.

Answer 15

• Calcium - Ca2+.
• Sodium - Na+.
• Potassium - K+.
• Hydrogen - H+.
• Ammonium - NH 4+.

Question 16

Inorganic anions.

Answer 16

• Nitrate - NO-3.
• Hydrogen carbonate - HCO3-.
• Chloride - Cl-.
• Phosphate - PO3-4.
• Hydroxide - OH-.

Question 17

Calcium.

Answer 17

• Involved in transmission of nerve impulses at a synapse and muscle contraction.

Question 18

Sodium.

Answer 18

• Transmission of nerve impulses along a neuron and for selective absorption of glucose.

Question 19

Potassium.

Answer 19

• Used in guard cells to open stomata and activate enzymes needed for photosynthesis in plant cells.

Question 20

Glucose.

Answer 20

• Main source of energy in animal and plants.
• Energy from between bonds can be used to produce ATP in aerobic and anaerobic respiration.
• Soluble.

Question 21

Forming a disaccharide.

Answer 21

• Hydroxyl group from one monosaccharide joins to the H atom from the hydroxyl group of the other monosaccharide.
• A molecule of water is released.
• Condensation reaction that forms a glycosidic bond between monosaccharides.

Question 22

Test for reducing sugar.

Answer 22

1. Heat sample with Benedict’s reagent.
2. Sample forms brick red precipitate = reducing sugar.

Question 23

Test for non-reducing sugar.

Answer 23

1. Heat sample with Benedict’s reagent.
2. Sample= blue (no reducing sugar present).
3. Heat sample with dilute hydrochloric acid.
4. Neutralise sample with sodium hydrogen carbonate.
5. Heat sample with Benedict’s reagent.
6. Blue = no non-reducing sugar present.
   Brick-red = non-reducing sugar.

Question 24

Amino acids.

Answer 24

• Monomers of proteins.
• Carbon, hydrogen, oxygen, nitrogen (occasionally sulphur).
• 20 different amino acids - 9 = essential.
• 2 amino acids = dipeptide.
• Protein = 1+ polypeptides.
• Hydroxyl group (-COOH) + amine group (-NH2) + R group (varies between amino acids).

Question 25

Formation of dipeptides.

Answer 25

• Peptide bond.
• Hydroxyl group in carbolic group of one amino acid reacts with hydrogen group in amine group of another amino acid.
• Releases water molecule.
• Condensation reaction.

Question 26

Primary structure of protein.

Answer 26

• Sequence of amino acids in polypeptide chain.
• Held together by peptide bonds.

Question 27

Secondary structure.

Answer 27

• Hydrogen bonds form between amino acid chain pulling into a coil - Alpha helix.
• Polypeptide chains lie parallel to each other joined by hydrogen bonds - Beta pleated sheet.

Question 28

Tertiary structure.

Answer 28

• Polypeptide chains further folds and coils into a 3D structure.
• Hydrogen bonds. - Individually weak but strong in high numbers.
• Ionic bonds. - Between positive and negative R groups.
• Disulphide bonds. -
• Hydrophobic and hydrophilic interactions.

Question 29

Water.

Answer 29

• 2 Hydrogen + 1 Oxygen.
• Covalent bonds.
• Oxygen = slightly negative.
• Hydrogen = slightly negative.
• Positive and negative poles. - dipolar molecule.

Question 30

Roles of water.

Answer 30

• Solvent.
• Temperature control.
• Cooling mechanism.
• Habitat.
• Transport.