Lipids

Question 1

What elements do lipids contain?

Answer 1

Carbon, hydrogen and oxygen

Question 2

What are lipids commonly known as?

Answer 2

Macromolecules- not built from monomers

Question 3

Why are lipids non polar?

Answer 3

Electrons in the outer orbital are evenly distributed so there are no positive/negative regions- lipids are insoluble in water (hydrophobic)

Question 4

What is a triglyceride made of?

Answer 4

One glycerol and three fatty acids

Question 5

What groups do glycerol and fatty acids belong to?

Answer 5

Glycerol- alcohol

Fatty acid- carboxylic acid

Question 6

How are ester bonds formed between a glycerol and fatty acids?

Answer 6

The hydroxyl groups on both molecules interact, forming 3 ester bonds and 3 water molecules (condensation reaction)
This reaction is called esterification

Question 7

How can triglycerides be broken down?

Answer 7

3 water molecules need to be supplied- hydrolysis reaction

Question 8

What is the difference between saturated and unsaturated fatty acids?

Answer 8

Saturated- no double bonds between carbon atoms
Unsaturated- there are double bonds between some of the carbon atoms
Monounsaturated (1) Polyunsaturated (2 or more)

Question 9

Why are fatty acids with no double bonds between carbon atoms called saturated?

Answer 9

They form the maximum number of bonds with hydrogen atoms

Question 10

Why are unsaturated fatty acids liquid at rt?

Answer 10

The presence of double bonds causes the molecule to kink/bend so it cannot pack so closely together. This is why they are described as oils (liquids)

Question 11

What elements do phospholipids contain?

Answer 11

Carbon, hydrogen, oxygen, phosphorus

Question 12

Why are phospholipids soluble in water?

Answer 12

The phosphate ions are negatively charged, making them polar and soluble in water (able to form H bonds with water)

Question 13

What is the structure of a phospholipid?

Answer 13

Glycerol, two fatty acids, one phosphate group

Question 14

What are the two parts to phospholipids?

Answer 14

Phosphate head- polar, hydrophilic

Fatty acid tails- non polar, hydrophobic

Question 15

How do phospholipids behave when they interact with water?

Answer 15

1- They form a layer with phosphate heads in the water and fatty acid tails sticking out of the water
2- They form a bilayer, hydrophobic tails point towards the centre, protected from the water by the phosphate heads

Question 16

Why do phospholipids play a key role in forming cell membranes?

Answer 16

By forming a bilayer, they are able to separate an aqueous environment from the aqueous cytosol within cells.

Question 17

Describe the structure of a sterol.

Answer 17

They have a four carbon ring structure with an OH group- have a dual hydrophobic/ hydrophilic nature

Question 18

What is the role of cholesterol?

Answer 18

It plays a role in the formation of cell membranes. It positions itself in between the phospholipids, adding to the stability of cell membranes and regulating their fluidity.

Question 19

Manufacture of cholesterol?

Answer 19

Body manufactures it in the liver/ intestines.

Steroid hormones/ bile are manufactured using cholesterol

Question 20

What are the roles of lipids?

Answer 20

1. Membrane formation
2. Hormone production
3. Electrical insulation
4. Cushioning to protect vital organs
5. Thermal insulation
6. Waterproofing

Question 21

What is the test to identify lipids?

Answer 21

Emulsion test- mix the sample with ethanol and then water, then shake
If a white emulsion forms on top, a lipid is present