1.3 Lipids

Question 1

Structure of triglycerides:

Answer 1

condensation of 1 glycerol and 3 fatty acids forming ester bond

Question 2

Are lipids non-polar or polar?

Answer 2

Non-polar

Question 3

Are lipids hydrophobic or hydrophilic?

Answer 3

Hydrophobic

Question 4

What are the two groups of lipids?

Answer 4

Triglycerides and phospholipids

Question 5

Structure of triglycerides:

Answer 5

1 glycerol and 3 fatty acids

Question 6

In triglycerides, what are the glycerol and the 3 fatty acids held together by?

Answer 6

Ester bonds

Question 7

Triglycerides are good for energy __________

Answer 7

storage

Question 8

How does the structure of triglycerides help them to be good for energy storage?

Answer 8

• The long fatty acid chains contain many C-H bonds
• so when triglycerides are oxidised, the bonds break
• releasing energy

Question 9

Triglycerides are useful for the storage of ________

Answer 9

water

Question 10

How does the structure of triglycerides make them useful for water storage?

Answer 10

• Triglycerides are hydrophobic
• so they do not cause water uptake in cells

Question 11

Triglycerides are useful for I_____________

Answer 11

insulation

Question 12

Why are triglycerides make them useful for insulation?

Answer 12

• Form part of the myelin sheath that surrounds nerve fibres
• increase the speed of nerve impulses

Question 13

Triglycerides are useful for P______________

Answer 13

protection

Question 14

Why are triglycerides useful for protection?

Answer 14

• The adipose tissue in mammals contains stored triglycerides
• this tissue helps to protect organs from the risk of damage

Question 15

How are triglycerides formed?

Answer 15

By esterification

Question 16

What is esterification?

Answer 16

The formation of an ester bond in a condensation reaction

Question 17

What are the components of phospholipids?

Answer 17

• Glycerol backbone
• 2 fatty acid chains
• A phosphate (PO4) group

Question 18

Are the fatty acid chains in phospholipids hydrophobic or hydrophilic?

Answer 18

Hydrophobic

Question 19

Is the phosphate head in phospholipids hydrophobic or hydrophilic?

Answer 19

Hydrophilic

Question 20

Do phospholipids contain both a saturated and unsaturated fatty acid chain?

Answer 20

YES

Question 21

What is a saturated fatty acid?

Answer 21

• Does NOT contain any double bonds
• The chains will be STRAIGHT

Question 22

What is an unsaturated fatty acid?

Answer 22

• DOES contain double bonds between (some) carbon atoms
• Fatty acid chains will be kinky

Question 23

What is the method for the test for lipids?

Answer 23

• Add 5cm3 of ethanol to the sample
• Shake to dissolve any lipid in the ethanol
• THEN add 5cm3 of water + shake

Question 24

What is the positive result for the test for lipids?

Answer 24

A cloudy-white emulsion

Question 25

What is the test for lipids called?

Answer 25

Emulsion

Question 26

The general structure of a fatty acid is RCOOH. Name the group represented by COOH.

Answer 26

Carboxylic acid

Question 27

Describe how you would test for the presence of a lipid in a liquid sample of food.

Answer 27

- Add ethanol and shake - Add water and shake - White emulsion

Question 28

Describe how a triglyceride molecule is formed.

Answer 28

- One glycerol and three fatty acids - 3 condensation reactions and removal of three molecules of water - 3 ester bonds formed

Question 29

The structure of a phospholipid molecule is different from that of a triglyceride. Describe how a phospholipid is different.

Answer 29

- Phosphate group - Has 2 fatty acids (instead of 3)

Question 30

Describe how a saturated fatty acid is different from an unsaturated fatty acid.

Answer 30

- Saturated = single bonds between carbons - Unsaturated = double bonds between carbons

Question 31

Which of the fatty acids, X or Y, in the figure above is unsaturated

Answer 31

Contains double bond between (adjacent) carbon atoms in hydrocarbon chain.

Question 32

The scientists expressed their results as Percentage of lipid in plasma membrane by mass. Explain how they would find these values.

Answer 32

mass of each lipid/ mass of all lipids x 100

Question 33

what is special about the R group of fatty acid

Answer 33

R-group of a fatty acid may be saturated or unsaturated

Question 34

What quality does hydrocarbon 'tails' give to fatty acids?

Answer 34

It makes them insoluble in water because the tails are hydrophobic.

Question 35

How are phospholipids similar to triglycerides?

Question 36

Contrast saturated and unsaturated fatty acids.

Answer 36

Saturated: Contain only single bonds Straight-chain molecules have many contact points Higher melting point = solid at room temperature Found in animal fats Unsaturated: Contain C=C double bonds ‘Kinked’ molecules have fewer contact points Lower melting point = liquid at room temperature Found in plant oils

Question 37

Compare phospholipids and triglycerides.

Answer 37

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

Question 38

contrast phospholipids and triglycerides.

Answer 38

phospholipids: 2 fatty acids & 1 phosphate group attached Hydrophilic head & hydrophobic tail Used primarily in membrane formation triglycerides: 3 fatty acids attached Entire molecule is hydrophobic Used primarily as a storage molecule (oxidation releases energy)