3.1.3 Lipids

Question 1

Describe how to test for Lipids in a sample

Answer 1

• Dissolve solid sample in ethanol
• Add an equal volume of water and shake
• Positive result: milky white emulsion forms

Question 2

How do Triglycerides form?

Answer 2

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

Question 3

Are Phospholipids and Triglycerides polymers?

Answer 3

No , there not made up of small repeating units and they’re macromolecules

Question 4

Compare Phospholipids and Triglycerides

Answer 4

• Both have a glycerol back bone
• Both contain the elements C,H and O
• Both formed by condensation reactions
• Both may be attached to a mixture of saturated , monounsaturated and polyunsaturated fatty acids

Question 5

Describe the structure and function of Phospholipids

Answer 5

Amphipathic molecule: glycerol backbone attached to 2 hydrophobic fatty acid tails and 1 hydrophilic polar phosphate head

• Forms phospholipid bilayer in water so is a component of membranes
• Tails can splay outwards so waterproofing

Question 6

Contrast Phospholipids and Triglycerides

Answer 6

Phospholipids
- 2 fatty acids and 1 phosphate group attached
- Hydrophilic head and hydrophobic tail
- Primarily used in membrane formation
Triglycerides
- 3 fatty acids attached
- Entire molecule is hydrophobic
- Used primarily as a storage molecule (oxidation releases energy)

Question 7

Relate the structure of Triglycerides to their function

Answer 7

• High energy: mass so high calorific value from oxidation
• Insoluble hydrocarbon chain so no effect on water potential of cells and is used for waterproofing
• Slow conductor of heat so thermal insulation e.g. the adipose tissue
• Less dense than water so buoyancy of aquatic animals