1.1.4 - Lipids

Question 1

what are lipids?

Answer 1

• non-polar compounds which contain C H and O
• compared to carbohydrates, they have much less oxygen

in proportion to C and H they have much less O

Question 2

comment on the solubility of lipids.

Answer 2

• non-polar so are insoluble in water
• dissolve in organic solvents such as alcohols

Question 3

how are triglycerides formed?

Answer 3

• the combination of 1 glycerol molecule and 3 fatty acid molecules.

Question 4

what differs across different lipids?

Answer 4

• glycerol molecule in a lipid is always the same but the fatty acid component varies.

Question 5

how do fatty acids join to glycerol?

Answer 5

• condensation reaction
• 3 molecules of water removed
• ester bonds formed

Question 6

what is a phospholipid?

Answer 6

• lipid in which one end of each molecule is soluble in water and the other end is not
• phosphate group in place of one fatty acid chain

Question 7

what is a saturated lipid and what are their properties?

Answer 7

• all carbon bonds are single bonds
• carbons bonded to maximum number of hydrogens
• straight chains (pack close together)
  -> high melting point - energy used to separate them
  -> solids at room temperature

Question 8

what is an unsaturated lipid and what are their properties?

Answer 8

• not all carbons bonded to maximum number of hydrogens
• contain 1 (monounsaturated) or more (polyunsaturated) C=C bonds
• chains cant be as close together
  -> low melting point
  -> liquids at room temp

Question 9

why is a triglyceride hydrophobic?

Answer 9

• the fatty acid tails do not have any oxygen atoms and do not interact with water so they are hydrophobic and non polar.

Question 10

what are waxes?

Answer 10

• lipids
• melt above 45℃

Question 11

what is the role of waxes?

Answer 11

• waterproofing

> animals = insect exoskeleton
plants = in the leaf’s cuticle

Question 12

what is the definition of hydrophilic

Answer 12

Polar
A molecule or ion that can interact with water molecules because of its charge

Question 13

what is the definition of hydrophobic

Answer 13

Non-polar
A molecule that cannot interact with water molecules because it has no charge

Question 14

what is the structure of a saturated fatty acid tail

Answer 14

• straight zigzag
• molecules can align readily so fats are solid

Question 15

what are lipids useful for?

Answer 15

useful for storage in mammals as they are semi solid at body temperature.

animal lipids often contain saturated fatty acids

Question 16

what is the structural difference between a saturated and unsaturated fatty acid chain?

Answer 16

• in unsaturated fatty acids, there is at least one c=c bond > the chain gets a kink

Question 17

why does the lipid not solidify readily in an unsaturated lipid?

Answer 17

• the molecules cannot align uniformly
  so the lipid does not solidify readily

this is why unsaturated lipids are oils (liquid at room temp)

Question 18

what do plant lipids often occur as?

Answer 18

• unsaturated lipids
• oils

e.g. olive and sunflower oil

Question 19

what are the 3 main lipids?

Answer 19

• triglycerides
• phospholipids
• waxes

Question 20

what is the function of triglycerides?

Answer 20

• ENERGY RESERVES
  > plans and animals as lipids contain more C-H bonds than carbohydrates

-

• THERMAL INSULATION
  > stored under skin - lipids insulate against heat loss in cold or heat gain in heat

-

• PROTECTION
  > stored around delicate organs e.g. kidneys to protect against damage

-

• PRODUCING METABOLIC WATER
  > triglycerides produce a lot when oxidised

Question 21

what is metabolic water

Answer 21

water released in the cells of an organism by its metabolic reactions

Question 22

what is the function of phospholipids

Answer 22

• STRUCTURAL
  > in biological membranes

-

• ELECTRICAL INSULATION
  > the myelin sheath that surrounds the axons of nerve cells
  > makes sure the electrical impulses stay within the nerves

Question 23

what is the function of waxes

Answer 23

• WATERPROOFING
  > reduce water loss in insect exoskeleton and cuticle of plant

Question 24

what is the test for fats and oils?

Answer 24

the emulsion test

Question 25

describe the emulsion test

Answer 25

- test sample mixed with absolute ethanol which dissolves any lipids present - shaken with equal volume of water - dissolved lipids come out of solution as they are insoluble in water - they form an emulsion making the sample cloudy white