Topic 1.5 - Lipids

Question 1

What are lipids made of ?

Answer 1

Carbon, hydrogen and oxygen. Like carbohydrates, but they have a higher proportion of hydrogen and lower proportion of oxygen.

Question 2

What are lipids? Are they soluble or insoluble?

Answer 2

A diverse group of compounds that are insoluble in water but soluble in organic solvents

Question 3

Why are lipids a good energy sources?

Answer 3

They contain twice the amount of energy as carbohydrates

Question 4

Where are lipids stored?

Answer 4

Adipose tissue (fat)

Question 5

What is the function of lipids?

Answer 5

• Source of energy
• Waterproofing - as lipids are insoluble in water
• Insulation - help retain heat
• Protection - stored around delicate organs

Question 6

Where can fat be used as an electrical insulator?

Answer 6

In the myelin sheath around nerve cells

Question 7

What are triglycerides made up of?

Answer 7

3 fatty acids bonded to glycerol

Question 8

What bond forms between the glycerol and fatty acid?

Answer 8

An ester bond

Question 9

What reaction occurs to form a triglyceride?

Answer 9

Condensation reactions, where H2O is removed and water forms as a product

Question 10

What happens when triglycerides break down?

Answer 10

They hydrolyse (water is added), producing glycerol and 3 fatty acids

Question 11

If there are no carbon-carbon double bonds in a fatty acid, what is it called?

Answer 11

Saturated

Question 12

If there is one carbon-carbon double bonds in a fatty acid, what is it called?

Answer 12

Monounsaturated

Question 13

If there is two or more carbon-carbon double bonds in a fatty acid, what is it called?

Answer 13

Polyunsaturated

Question 14

What happens to the lipid produced if the fatty acids have C=C bonds (double carbon-carbon bonds)?

Answer 14

They become oils at room temperature, as the double bond causes the molecule to bend and therefore cannot pack together as tightly.

Question 15

How is the structure of triglycerides suited to its function?

Answer 15

• Excellent source of energy
• Insoluble (due to being large and non-polar) - does not affect osmosis or water potential
• Provide an important source of water

Question 16

What are phospholipids made up of?

Answer 16

A phosphate, a glycerol and 2 fatty acids

Question 17

Is a phospholipid hydrophilic or hydrophobic?

Answer 17

It is amphipathic, both hydrophilic and hydrophobic

Question 18

Is a phospholipid polar or non-polar?

Answer 18

It is a polar molecule

Question 19

What do phospholipids play a key role in?

Answer 19

Forming cell membranes as they are able to separate the aqueous environment.

This is done by creating a bilayer of phospholipids, where the hydrophilic head faces the water and the hydrophobic tail is on the inside.

Question 20

What part of the phospholipid is hydrophilic?

Answer 20

The phosphate group (the ‘head’)

Question 21

What does ‘hydrophilic’ mean?

Answer 21

‘Water-loving’ - it interacts with water

Question 22

What part of the phospholipid is hydrophobic?

Answer 22

The fatty acids (the ‘tail’)

Question 23

What does ‘hydrophobic’ mean?

Answer 23

Water ‘hating’ - does not interact with water so it orientates itself away

Question 24

What are sterols?

Answer 24

Lipids that are neither fats nor oils

Question 25

What test is used to identify fats?

Answer 25

The emulsion test

Question 26

Using the emulsion test, how would you know that the sample contains lipids?

Answer 26

A cloudy-white colour

Question 27

How is the structure of a phospholipid related to its function?

Answer 27

• They are polar - forms a bilayer in cell membranes to form a barrier between the inside and outside of the cell
• The hydrophilic heads - interacts with the polar molecules, so this allows the passage of proteins, water and many other molecules to go in and out of the cell
• Allows them to form glycolipids (lipids + carbohydrates) - important in cell recognition

Question 28

How would you conduct a test for lipids?

Answer 28

• For every 2cm cubed there is of the sample, add 5cm cubed of ethanol
• Shake thoroughly to dissolve any potential lipids
• The presence of a lipid will be indicated by the cloudy-white colour formed in tube