3.1.3 Lipids

Question 1

What do lipids consist of?

Answer 1

Glycerol and fatty acids

Question 1

Briefly describe what lipids are and some of their properties

Answer 1

-macromolecules that consist of carbon, hydrogen and oxygen atoms only
-they are insoluble in water
-they exist as fats, oils and waxes
-they are poor conductors of heat
-they are a good source of energy

Question 2

What are the two groups of lipids?

Answer 2

Triglycerides and phospholipids

Question 3

What is an unsaturated fatty acid?

Answer 3

-one which consists of one or more carbon-carbon double bonds
-usually liquid at room temperature

Question 3

What is a saturated fatty acid?

Answer 3

-a fatty acid that consists of only carbon-carbon single bonds
-usually is solid at room temperature

Question 3

What is the functional group of a fatty acid?

Answer 3

RCOOH - the ‘r’ group determines the length of the hydrocarbon chain, and therefore which fatty acid it is.

Question 4

What is a monounsaturated fatty acid?

Answer 4

-a fatty acid with only one carbon-carbon double bond

Question 4

What is a polyunsaturated fatty acid?

Answer 4

-a fatty acid with multiple carbon-carbon double bonds

Question 5

What is a triglyceride?

Answer 5

-a non-polar, hydrophobic molecule
-a type of lipid
-formed by a condensation reaction called esterification, between 1 glycerol molecule and 3 fatty acids.
-this reaction forms ester bonds

Question 6

Describe the reaction to form a triglyceride?

Answer 6

-condensation reaction known as esterification
-forms ester bonds
-reaction between 1 glycerol molecule and 3 fatty acid molecules
-this forms a triglyceride and 3 water molecules

Question 7

Outline the function of a triglyceride as an insulator

Answer 7

-makes up part of the myelin sheath around neurones, which provides insulation to increase the speed of transmission of nerve impulses
-acts as insulation under the skin to prevent heat loss from the body

Question 8

Outline the function of a triglyceride as a storage molecule

Answer 8

-they store more energy per gram than proteins and carbohydrates, due to their long hydrocarbon chains, making them a useful energy store
-they are hydrophobic so do not cause osmotic water intake to cells, so more can be store
-oxidation of the C-H bonds releases water molecules during respiration
-they form insoluble droplets inside cells making them easy to store

Question 9

Outline the function of triglycerides for protection

Answer 9

-protect organs from damage in mammals
-buoyant which increases floating ability, due to their low density.

Question 10

What is a phospholipid?

Answer 10

-a type of lipid formed from glycerol, fatty acids and a phosphate ion
-they are formed in a condensation reaction, known as esterification, and form ester bonds.

Question 11

Describe the reaction which forms phospholipids?

Answer 11

-a condensation reaction known as esterification
-forms ester bonds
-1 glycerol molecule reacts with 2 fatty acid molecules, and a phosphate ion
-releases 3 water molecules when formed

Question 12

Describe the function of a phospholipid

Answer 12

-make up the main component of a cell membrane, as they form monolayers and bilayers in water (as the hydrophilic head attracts to water, and the hydrophobic head repels it)
-This controls water, and water soluble molecules from entering or leaving the cell

Question 12

What are the properties of a phospholipid?

Answer 12

-The phosphate group gives the phospholipid a very negative polar head, which is hydrophilic
-the fatty acid tails are non-polar, and hydrophobic

Question 13

State 5 differences between a phospholipid and a triglyceride

Answer 13

-triglycerides are made up of 3 fatty acids, whereas phospholipids are made up of 2 fatty acids
-triglycerides do not have a phosphate group, whereas phospholipids do
-triglycerides have hydrophobic fatty acids, but phospholipids have hydrophobic fatty acids and a hydrophilic head
-triglycerides are non-polar, whereas phospholipids have a very negative polar head
-the main function of triglycerides is energy storage, whereas the main function of phospholipids is that they are the main component of cell membranes

Question 14

State and explain the results of the ethanol test for lipids

Answer 14

-if lipids are present, a cloudy white emulsion is produced

This is because lipids are not soluble in water, so ethanol is added. When water is added, tiny white droplets of lipids form which is the cloudy white emulsion we see.

Question 14

What are 4 similarities between triglycerides and phospholipids?

Answer 14

-both contain one molecule of glycerol
-both have ester bonds, formed by condensation reaction known as esterification
-both release 3 water molecules when formed
-both made through condensation reactions

Question 15

Describe the biochemical test for lipids

Answer 15

-add ethanol and shake
-then add water and shake again