Topic 1.3 Lipids

Question 1

Name two groups of lipid

Answer 1

Triglycerides and phospholipids

Question 2

Describe the structure of a fatty acid (RCOOH)

Answer 2

● Variable R-group - hydrocarbon chain (this may be saturated or unsaturated)
● -COOH = carboxyl group

Question 3

Describe the difference between saturated and unsaturated fatty acids

Answer 3

● Saturate - no C=C double bonds in hydrocarbon chain → all carbons fully saturated with hydrogen
● Unsaturated - one or more C=C double bond in hydrocarbon chain (creating a bend / kink)

Question 4

Describe how triglycerides form

Answer 4

● 1 glycerol molecule and 3 fatty acids
● 3 condensation reactions
● Removing 3 water molecules
● Forming 3 ester bonds

Question 5

Explain how the properties of triglycerides are related to their structure
Function: energy storage

Answer 5

● High ratio of C-H bonds to carbon atoms in hydrocarbon chain
○ So used in respiration to release more energy than the same mass of carbohydrates

● Hydrophobic / non-polar fatty acids so insoluble in water (clump together as droplets, tails inwards)
○ So no effect on water potential of cell (or can be used for waterproofing)

Question 6

Describe the difference between the structure
of triglycerides and phospholipids

Answer 6

One of the fatty acids of a triglyceride is
substituted by a phosphate-containing group

Question 7

Describe how the properties of phospholipids relate to their structure

Answer 7

Function: form a bilayer in cell membrane, allowing diffusion of lipid-soluble (non-polar) or very small
substances and restricting movement of water-soluble (polar) or larger substances

● Phosphate heads are hydrophilic
○ Attracted to water so point to water (aqueous environment) either side of membrane
● Fatty acid tails are hydrophobic
○ Repelled by water so point away from water / to interior of membrane

Question 8

Describe the test for lipids

Answer 8

1. Add ethanol, shake (to dissolve lipids), then add water
2. Positive result = milky white emulsion