Lipids

Question 1

Name two groups of lipids

Answer 1

Triglycerides and phospholipids.

Question 2

Describe the structure of a fatty acid (RCOOH)

Answer 2

• Variable R-group - hydrocarbon chain ( saturated or unsaturated ).
• -COOH = carboxyl group.

Question 3

Describe the difference between saturated and unsaturated fatty acids

Answer 3

• Saturated: no C=C double bonds in hydrocarbon chains; all carbons are saturated with hydrogen.
• Unsaturated: one or more C=C bonds in the hydrocarbon chain ( creating bend/kink ).

Question 4

Describe how triglycerides form

Answer 4

• 1 glycerol molecule and 3 fatty acids.
• Condensation reaction
• Removing water molecules
• Forming 3 ester bonds

Question 5

Explain how the properties of triglycerides are related to their structure.

Answer 5

Function: energy storage
High ratio of C-H bonds to carbon atoms in hydrocarbon atoms ;
- 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 ).
- So, there is no effect on the water potential of the cell ( or it 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 the cell membrane, allowing diffusion of lipid-soluble ( non-polar ) or very small substances and restricting movement of water-soluble (polar).

Question 8

Are phosphate heads hydrophilic ?

Answer 8

They are attracted to water so point to water (aqueous environment) either side of membrane.

Question 9

Are fatty acids hydrophobic ?

Answer 9

They are repelled by water so point away from water / to interior of membrane.

Question 10

Describe the test for lipids ?

Answer 10

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