lipids

Question 1

Describe how triglycerides form

Answer 1

The condensation reaction between 1 molecule of glycerol and 3 fatty acids to form an ester bond

Question 2

Describe a method for how to test for lipids in a sample

Answer 2

1. Dissolve solid samples in ethanol
2. Add an equal volume of water and shake
3. Positive result = milky white emulsion forms

Question 3

Describe the structure of saturated fatty acids

Answer 3

1. Contain only single bonds
2. Straight chain molecules which have many contact points
3. Higher melting points so are solid at room temperature
4. Found in animal fats

Question 4

Describe the structure of unsaturated fatty acids and where they are often found

Answer 4

1. Contain C=C double bonds
2. Kinked molecules which have fewer contact points
3. Lower melting point so liquid at room temperature
4. Found in plant oils

Question 5

Explain how the structure of triglycerides adapts them for their function

Answer 5

1. High energy to mass ratio so have high calorific value from oxidation for energy storage
2. Insoluble hydrocarbon chain so they have no effect on water potential of cells and are used for waterproofing
3. Slow conductor of heat so can be used for thermal insulation
4. Less dense than water for the buoyancy of aquatic animals

Question 6

Describe the structure of phospholipids

Answer 6

An amphipathic molecule made of a glycerol backbone attached to 2 hydrophobic fatty acid tails and 1 hydrophilic polar phosphate head

Question 7

Describe the functions of phospholipids

Answer 7

1. Forms phospholipid bilayer in water so is a component of cell membranes
2. Tails can splay outwards for waterproofing

Question 8

List the similarities between phospholipids and triglycerides

Answer 8

1. Both have a glycerol backbone
2. Both may be attached to a mixture of saturated, monounsaturated and polyunsaturated fatty acids
3. Both contain elements C, H, O
4. both are formed by condensation reactions

Question 9

List the dissimilarities between phospholipids and triglycerides

Answer 9

1. Phospholipids have 2 fatty acids and 1 phosphate group attached whereas triglycerides have 3 fatty acids attached
2. Phospholipids are amphipathic because they contain a hydrophobic tail and hydrophilic tail, triglycerides are entirely hydrophobic
3. Phospholipids are used in membrane formation whereas triglycerides are used as energy storage molecules

Question 10

Are phospholipids and triglycerides polymers?

Answer 10

No, they are macromolecules

Question 11

What are saturated fatty acids?

Answer 11

Saturated fatty acids contain no double carbon bonds.

Question 12

What are non-saturated fatty acids?

Answer 12

Non-saturated fatty acids contain 1 or more double carbon bonds in the hydrocarbon tail.