3.1.3 Lipids Flashcards
Describe how to test for lipids in a sample.
- Dissolve solid samples in ethanol.
- Add an equal volume of water and shake.
- Positive results: milky white emulsion forms.
How do triglycerides form?
condensation reaction between 1 molecule of glycerol and 3 fatty acids forms ester bonds.
Contrast saturated and unsaturated fatty acids.
Saturated
- Contain only single bonds
- Straight-chain molecules have many contact points
- Higher melting point = solid at room temperature
- Found in animal fats
Unsaturated
- Contain C=C double bonds
- ‘Kinked’ molecules have fewer contact points
- Lower melting points = liquid at room temperature
- Found in plant oils
Relate the structure of triglycerides to their functions.
- High energy:mass ratio = high calorific value from oxidation (energy storage)
- Insoluble hydrocarbon chain = no effect on water potential of cells and used for waterproofing
- Slow conductor of heat = thermal insulation (e.g. adipose tissue)
- Less dense than water = buoyancy of aquatic animals
Describe the structure and function of phospholipids.
Amphipathic molecule: glycerol backbone attached to 2 hydrophobic fatty acid tails and 1 hydrophilic polar phosphate head.
- Forms phospholipid bilayer in water = component of membranes.
- Tails can splay outwards = waterproofing.
Compare phospholipids and triglycerides.
- Both have glycerol backbone.
- Both may be attached to a mixture of saturated, monounsaturated and polyunsaturated fatty acids.
- Both contain the elements C, H, O.
- Both formed by condensation reactions.
Contrast phospholipids and triglycerides.
Phospholipids
- 2 fatty acids and 1 phosphate group attached
- 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 (oxidation releases energy)
Are phospholipids and triglycerides polymers?
No; they are not made from a small repeating unit. They are macromolecules.
