3.1.3 Lipids

Question 1

Name 2 groups of lipids

Answer 1

Triglycerides and phospholipids

Question 2

Describe how triglycerides are formed

Answer 2

1. Made of 1 glycerol molecules and 3 fatty acids
2. Condensation reactions.
3. Removing 3 water molecules.
4. Forming 3 ester bonds.

Question 3

Describe the differences between saturated and unsaturated fatty acids

Answer 3

• The R-group of a fatty acid may be saturated or unsaturated.
• Saturated: no C=C double bonds in hydrocarbon chain; all carbons fully saturated with hydrogen.
• Unsaturated: one or more C=C double bonds in hydrocarbon chain.

Question 4

Describe the structure of a phospholipid

Answer 4

In phospholipids, one of the fatty acids of a triglyceride is substituted by a phosphate-containing group.

Question 5

Describe the emulsion test for lipids

Answer 5

Add ethanol (alcohol) and shake (to dissolve lipids).
* Then add water.
* Shake again
* Positive: milky/white emulsion

Question 6

Describe how the properties of triglycerides relate to their structure.

Answer 6

• Triglycerides: energy storage molecules / energy source.
• High ratio of C-H bonds to C atoms in hydrocarbon tail.
• Release more energy than same mass of carbohydrates.
• Insoluble in water (clump together as droplets)
• No effect on water potential of cell i.e. no osmotic effect.

Question 7

Describe how the properties of phospholipids relate to their structure.

Answer 7

Phospholipids: form cell membrane (phospholipid bilayer); allowing movement of non-polar / lipid soluble / small molecules down a concentration gradient.
* Phosphate heads are polar / hydrophilic.
* Attracted to water → orient to aqueous environment either side of membrane.
* Fatty acid tails are non-polar / hydrophobic.
* repelled by water → orient to interior of membrane.