3.1.3 Lipids

Question 1

Describe how to test for lipids in a sample

Answer 1

Dissolve solid samples in ethanol
Add an equal volume of water and shake
Positive result - milk white emulsion forms

Question 2

How do triglycerides form

Answer 2

Condensation reaction between 1 molecule of glycerol and 3 fatty acids forms ester bonds

Question 3

Contrast saturated and unsaturated fatty acids

Answer 3

Saturated:
Only single bonds
Straight chain molecules have many contact points
Higher mtp - solid at room temp
Found in animal fats

Unsaturated
Contain C=C double bonds
Kinked molecules have fewer contact points
Lower mtp - liquid at room temp
Found in plant oils

Question 4

Relate the structure of triglycerides to their functions

Answer 4

High energy:mass ratio = high calorific value from oxidation
Insoluble hydrocarbon chain = no effect on water potential of cells and used for waterproofing
Slow conductor of heat = thermal insulation
Less dense than water = buoyancy of aquatic animals

Question 5

Describe the structure and function of phosopholipids

Answer 5

Amphipathic molecule: glycerol backbone attached to 2 hydrophobic fatty acid tails and 1 hydrophilic polar phosphate head
- Forms phospholipid bilayer in water
- Tails can splay outwards - waterproofing

Question 6

Compare phospholipids and triglycerides

Answer 6

Both have glycerol backbone
Both may be attatched to a mixture of saturated, monounsaturated and polyunsaturated fatty acids
Both contain elements C, H, O
Both formed by condensation reactions

Question 7

Contrast phospholipids and triglycerides

Answer 7

Phospholipids
2 fatty acids 1 phosphate group
Hydrophilic head and hydrophobic tail
Used primarily in membrane formation

Triglycerides
3 fatty acids attached
Entire molecule is hydrophobic
Used primarily as a storage molecule

Question 8

Are phospholipids and triglycerides polymers

Answer 8

No; they are not made from a small repeating unit, they are macromolecules