Chapter 3 - Lipids

Question 1

What chemical elements do lipids contain?

Answer 1

carbon (C), hydrogen (H), and oxygen (O)

However, lipids contain a much lower proportion of oxygen than carbohydrates.

Question 2

Why are lipids NOT considered polymers?

Answer 2

They are not made made of long chains of monomers

Question 3

What are lipids?

Answer 3

Large, complex molecules known as macromolecules.

Question 4

Give 5 functions of lipids:

Answer 4

Energy supply
Structural components
Waterproofing
Insulation
Protection

Question 5

How are lipids an energy supply?

Answer 5

They can be oxidized to provide energy to cells.

Question 6

How are lipids a structural component?

Answer 6

Phospholipids are used in cell membranes.

Question 7

How are lipids waterproofing?

Answer 7

Insoluble lipids are used to form water-resistant barriers.

Question 8

How are lipids insulation?

Answer 8

Lipids can help retain heat or act as electrical insulators.

Question 9

How are lipids protection?

Answer 9

Delicate organs are surrounded by a layer of fat.

Question 10

Describe the structure of lipids

Answer 10

Most lipids are made up of fatty acids combined with an alcohol (usually glycerol).

Question 11

Describe the structure of fatty acids

Answer 11

Fatty acids consist of a carboxyl group (-COOH) attached to a hydrocarbon chain (R group).

Question 12

What are the two types of fatty acids?

Answer 12

saturated fatty acids and unsaturated fatty acids

Question 13

Describe saturated fatty acids

Answer 13

These have hydrocarbon chains that are ‘saturated’ with hydrogen, meaning all carbon atoms are bonded to the maximum number of hydrogen atoms.
The hydrocarbon chain has no carbon-carbon double bonds.

Question 14

Do lipids that contain saturated fatty acids have higher melting points or not and what does this mean?

Answer 14

Yes and and so are usually solid at room temperature (fats).

Question 15

Do lipids that contain unsaturated fatty acids have lower melting points and what does this mean?

Answer 15

Yes and so are usually liquid at room temperature (oils).

Question 15

Describe unsaturated fatty acids

Answer 15

These have hydrocarbon chains that do not contain the maximum number of hydrogen atoms bonded to the carbon atoms.
The hydrocarbon chain has at least one carbon-carbon double bond, which causes the chain to kink.

Question 16

What 2 forms could unsaturated fatty acids take?

Answer 16

Monounsaturated - One double bond.
Polyunsaturated - Two or more double bonds.

Question 17

What are the three types of lipids

Answer 17

Triglycerides, Phospholipids & Cholesterol

Question 18

What are triglycerides?

Answer 18

They are non-polar macromolecules used as a store of energy in animals, plants, and some bacteria.

Question 19

What is the structure of triglycerides

Answer 19

Formed from on molecule of glycerol and 3 fatty acid chains.
Each fatty acid tail contains a hydrocarbon chain (R) which can vary in length and may be saturated or unsaturated.

Question 20

What are features that allow triglycerides to store energy efficiently?

Answer 20

1. Long hydrocarbon tails
2. Low mass to energy ratio
3. Insoluble
4. High ratio of hydrogen to oxygen atoms

Question 21

How does having long hydrocarbon tails help triglycerides do their job?

Answer 21

Their many carbon-hydrogen bonds can be broken to release energy.

Question 22

How does having low mass to energy ratio help triglycerides do their job?

Answer 22

Lots of energy can be stored in a small volume.

Question 23

How does being insoluble help triglycerides do their job?

Answer 23

They do not affect the water potential of cells as they are large and non-polar.

Question 24

How does having high ratio of hydrogen to oxygen atoms help triglycerides do their job?

Answer 24

Because triglycerides will release water when oxidised.

Question 25

How are triglycerides synthesised?

Answer 25

via condensation reactions

Question 26

How are triglycerides broken down?

Answer 26

via hydrolysis reactions

Question 27

Describe a condensation reaction that makes a triglyceride

Answer 27

The hydroxyl groups (OH) on the glycerol and on the three fatty acids react together to release three water molecules (H2O). This results in three ester bonds between the glycerol and the fatty acids.

Question 28

Describe a hydrolysis reaction that breaks down a triglyceride

Answer 28

The addition of three water molecules (H2O) breaks the ester bonds. This separates the glycerol and the fatty acids.

Question 29

What is a phospholipid?

Answer 29

A phospholipid is a type of lipid used as a structural component of the cell membrane.

Question 30

Describe the structure of a phospholipid

Answer 30

They are similar to triglycerides except one of the fatty acid tails is replaced by a phosphate group. They have a: hydrophilic 'head' - This contains glycerol and phosphate. And a hydrophobic 'tail' - This contains fatty acids.

Question 31

How are the head ad the tail in a phospholipid different to each other?

Answer 31

The phosphate group is polar and so attracts water (hydrophilic) whereas the fatty acid tails repel water (hydrophobic).

Question 32

How do phospholipids align themselves when placed in water?

Answer 32

When phospholipids are placed in water, they arrange themselves into a double layer (bilayer) so that the hydrophilic heads are facing out (towards the water) and the hydrophobic tails are facing in (away from the water). This arrangement creates a hydrophobic centre in the bilayer so that water-soluble substances cannot pass through.

Question 33

What is cholesterol and what is it used for?

Answer 33

Cholesterol is a type of lipid known as a sterol and is used by animal cells to increase the stability of the cell membrane. Cholesterol is also used to make vitamin D, steroid hormones, and bile.

Question 34

Describe the structure of cholesterol

Answer 34

Like phospholipids, cholesterol is a polar molecule. The hydroxyl group (OH) is hydrophilic whereas the rest of the molecule is hydrophobic

Question 35

What is the role of cholesterol in the cell membrane?

Answer 35

Cholesterol binds to phospholipid fatty acid tails, causing the phospholipids to pack more closely together. This reduces the fluidity of the cell membrane, and increases the stabilty.