3.1.3 Lipids

Question 1

Describe how to test for lipids in a sample.

Answer 1

1. Dissolve solid samples in ethanol
2. Add an equal volume of COLD water and shake.
3. 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
forms ester bonds

Question 3

contrast saturated and unsaturated fatty acids.

Answer 3

saturated:
- contain only single bonds
- straight chain molecules
- many contact points
- higher melting point = solid at room temp.
- found in animal fats
unsaturated:
- contain C=C double bonds
- ‘Kinked’ molecules
- have fewer contact points
- lower melting point = liquid at room temp.
- in plant oils

Question 4

relate the structure of triglycerides to their function.

Answer 4

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
less dense than water = buoyancy of aquatic animals

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 belayed in water = component of membranes
- tails can splay outwards = waterproofing

Question 6

what are the similarities between phospholipids and triglycerides.

Answer 6

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

Question 7

what are the differences between phospholipids and triglycerides?

Answer 7

• phospholipids: 2 fatty acids, triglycerides: 3
• phospholipid: phosphate group, triglycerides: no phosphate group
• phospholipid: hydrophobic tails & hydrophilic head, triglycerides: entire molecule is hydrophobic
  -phospholipids: used primarily in membrane formation, triglycerides: used primarily as a storage molecule (oxidation releases energy)

Question 8

are phospholipids and triglycerides polymers? why?

Answer 8

no
they are made from a small repeating unit
they are called macromolecules