3.5- Lipids

Question 1

What are lipids?

Answer 1

Made up of carbon, hydrogen and oxygen.

• non polar molecules as electrons on the outer orbitals are evenly distributed. Therefore lipids are not soluble in water.
• fats = solid at room temp. Oils= liquid at room temp.

Lipids are large molecules known as macromolecules. They are not built from repeating units or monomers.

Question 2

Triglycerides.

Answer 2

A triglyceride is made by combining one glycerol molecule with three fatty acids.
- glycerol = alcohol
- fatty acids = carboxylic acids (-COOH)
Esterification:
Hydroxyl groups from both elements interact to form 3 water molecules (condensation reaction).
Ester bonds are formed.

To break down triglycerides 3 water molecules are needed to reverse the reaction= hydrolysis.

Question 3

What are the differences between saturated and unsaturated fatty acids?

Answer 3

Saturated:

• no double bonds
• can pack closely together.

Unsaturated:
-double bonds present;
      > 1= monounsaturated 
      > 2+ = polyunsaturated
- double bonds cause the chain to bend so they can’t pack together.
-liquids at room temp.(oils)

Question 4

Phospholipids.

Answer 4

Modified triglycerides- one fatty acid chain is replaced with a phosphate group.
Contain CHO and phosphorus.

• phosphate ions are negatively charged so are soluble.
• have a hydrophilic head (polar) and a hydrophobic tail (non-polar).
• called surfactants: form layer on the surface of water with phosphate head in water and fatty acid tail sticking out.
• play a key role in forming cell membranes due to their bilayer arrangement.

Question 5

Sterols.

Answer 5

Also known as steroid alcohols.
Type of lipid found in cells- neither fats or oil.
-complex alcohol molecules based on 4 carbon ring structure with OH group at one end.
Hydroxyl group= hydrophilic (polar)
Rest of molecule= hydrophobic (non-polar)

Question 6

Cholesterol

Answer 6

Is a sterol.
Has a role in the formation of cell membranes.
-made in the liver and intestines.
- stabilises cell membranes and regulates fluidity by keeping membranes fluid at low temps and stopping them becoming too fluid at high temperatures.

Vit D, steroid hormones and bile manufactured using cholesterol.

Question 7

What are the roles of lipids?

Answer 7

• membrane formation + creation of hydrophobic barriers.
• hormone production.
• electrical insulation (necessary for impulse transmission)
• waterproofing (eg. Birds feathers)

Stored under the skin + around vital organs so also provide:

• thermal insulation to stop heat loss.
• cushioning to protect organs.
• buoyancy for aquatic organisms.

Question 8

How are lipids identified?

Answer 8

Emulsion test:

1. Mix the sample with ethanol.
2. Mix solution with water + shake.
3. If white emulsion forms as a layer on top= lipid present.