3.1.3 Lipids

Question 1

How are triglycerides formed?

Answer 1

By the condensation of one molecule of glycerol and three molecules of fatty acid forming ester bonds.

Question 2

What type of reaction forms ester bonds between glycerol and fatty acids?

Answer 2

Condensation reaction.

Question 3

What bond is formed between glycerol and a fatty acid?

Answer 3

Ester bond.

Question 4

What is the general formula for a fatty acid?

Answer 4

RCOOH.

Question 5

How does the R-group of a fatty acid affect its properties?

Answer 5

If the R-group is saturated there are only single bonds between carbon atoms if it is unsaturated there are one or more double bonds between carbon atoms.

Question 6

How do phospholipids differ from triglycerides in structure?

Answer 6

One fatty acid of a triglyceride is replaced by a phosphate-containing group.

Question 7

Why are triglycerides insoluble in water?

Answer 7

Fatty acid tails are hydrophobic so triglycerides do not mix with water.

Question 8

How do triglycerides function as energy storage molecules?

Answer 8

They have a high ratio of energy-storing carbon-hydrogen bonds to carbon atoms and release energy when oxidised.

Question 9

How do phospholipids interact with water?

Answer 9

They form a bilayer with hydrophilic phosphate heads facing water and hydrophobic fatty acid tails facing inward.

Question 10

Why are phospholipids important in cell membranes?

Answer 10

They form a bilayer that acts as a barrier to water-soluble substances.

Question 11

Describe the emulsion test for lipids.

Answer 11

Add ethanol then shake add water and shake again a white emulsion indicates the presence of lipids.

Question 12

How do the structures of triglycerides and phospholipids relate to their properties?

Answer 12

Triglycerides are hydrophobic and store energy due to their many carbon-hydrogen bonds phospholipids form bilayers due to their hydrophilic heads and hydrophobic tails.

Question 13

How are triglycerides formed

Answer 13

1. One glycerol and three fatty acids;
2. Condensation(reactions) and removal of three molecules of water;
3. Ester bond(s) (formed);

Question 14

Phospholipids compared with
Triglycerides (8)

Answer 14

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 15

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

Answer 15

1. Condensation reaction
2. Between glycerol and fatty acid

Question 16

Test for a lipid

Answer 16

1. (Mix / shake sample) with ethanol, then water; Sequence is important
2. White / milky (emulsion);