Lipids

Question 1

What elements are lipids made of?

Answer 1

Carbon, hydrogen and a little oxygen

Question 2

Why are lipids hydrophobic?

Answer 2

Because they have little oxygen, meaning they have less polar bonds, therefore making them hydrophobic

Question 3

Do lipids have more or less hydrogen in them than carbohydrates?

Answer 3

More

Question 4

Are lipids soluble or insoluble in water?

Answer 4

Insoluble

Question 5

What are lipids soluble in?

Answer 5

• Ethanol
• Organic solvents

Question 6

What are the two types of lipid?

Answer 6

• Fats -> solid at RT (animals produce mostly fats)
• Oils -> liquid at RT (plants produce mostly oils)

Question 7

What are 7 functions of lipids?

Answer 7

• Dense energy source
• Insulation
• Protection
• Waterproofing
• Metabolic water
• Buoyancy
• Cell membranes

Question 8

Why are lipids good for storage?

Answer 8

• Insoluble -> they do not disperse
• They don’t affect water potential
• Energy rich (produce 2x as much energy as carbohydrates)

Question 9

How are lipids used for insulation?

Answer 9

• Fats are slow conductors of heat so are stored underneath the skin of endothermic to maintain a constant body temperature
• Very important for acquatic organisms
• Also provides electrical insulation around nerves

Question 10

How are lipids used for protection?

Answer 10

Fat is stored around delicate organs like the kidneys

Question 11

How are lipids used for waterproofing?

Answer 11

• Water conservation is important to all terrestrial organisms
• Plants and insects have a
  waxy cuticle
• Mammals secrete an oily substance from sebaceous glands. They repel water so prevent water loss.

Question 12

How are lipids used as a water source?

Answer 12

Breakdown of triglycerides can provide metabolic water which desert
animals can use

Question 13

How are lipids used for buoyancy?

Answer 13

Lipids are less dense than water so insulated aquatic animals are buoyant (float) -> aids breathing

Question 14

How are lipids used in cell membranes?

Answer 14

Phospholipids are a component of cell surface membranes. They add flexibility and act as a barrier in the cell.

Question 15

What are the types of lipid?

Answer 15

• Simple -> triglycerides (fats, oils), waxes, steroids (hormones that derive from cholesterol)
• Complex -> phospholipids (similar to triglycerides and a component of cell surface membranes), glycolipids

Question 16

What are triglycerides?

Answer 16

• Made of 3 fatty acids and a glycerol molecule
• Fatty acids contain a carboxyl group (COOH), hence acid
• Uncharged molecule, so insoluble jn water and hydrophobic

Question 17

How are triglycerides formed?

Answer 17

• In a condensation reaction, the COOH group of the fatty acids react with the OH group of the glycerol molecule, which forms an ester bond
• Water is also formed
• Covalent linkage, so very strong

Question 18

What is the formula of glycerol?

Answer 18

C₃H₅(OH)₃

Question 19

What do the properties of triglycerides depend on?

Answer 19

• The fatty acids
• Because glycerol only has one form

Question 20

What is the difference between saturated and unsaturated fats?

Answer 20

• Saturated -> they don’t have a C=C double bond
• Unsaturated -> that have one or more C=C double bonds

Question 21

What do mono and polyunsaturated fats mean?

Answer 21

• monounsaturated -> one C=C double bond
• polyunsaturated -> multiple C=C double bonds

Question 22

What do the C=C double bonds do to the fatty acids?

Answer 22

• Makes the fatty acids bend
• So they can’t pack as closely and the triglyceride is more liquid (oil)
• Double bonds reduce the melting point

Question 23

What are waxes?

Answer 23

• Lipid molecules where the hydrocarbon chain is linked to an alcohol and not glycerol
• (not digested by animals)

Question 24

What is the main use of waxes?

Answer 24

• Waterproof covering in living organisms -> e.g outer cuticle on leaves

Question 25

Why are steroids a type of lipid?

Answer 25

- So that they can pass directly through phospholipid bilateral (including nuclear envelope) - So can bind to target receptor in nucleus and can act directly on DNA

Question 26

What is the structure of cholesterol and what does this structure allow them to do?

Answer 26

- Made of 4 carbon rings joined together - Small narrow structure allow them to sit between phospholipids in membranes

Question 27

Where is most cholesterol made?

Answer 27

Most is made in the liver (also comes from diet)

Question 28

What two steroid hormones are made from cholesterol?

Answer 28

- Oestrogen - Testosterone

Question 29

What vitamin is made from cholesterol?

Answer 29

Vitamin D (important in calcium absorption, deficiency= rickets)

Question 30

What does cholesterol do in plasma membranes?

Answer 30

- Regulates membrane fluidity

Question 31

How do you test for lipids?

Answer 31

- Add ethanol and shake well - Cloudy white -> positive result

Question 32

Why does the ethanol test work?

Answer 32

- Lipids are insoluble in water and soluble in ethanol (an alcohol) - After lipids have been dissolved in ethanol and then added to H2O, they will form tiny dispersed droplets in the water (emulsion) - Droplets scatter light as it passes through the water so it appears white and cloudy

Question 33

Give three differences between saturated and unsaturated fats?

Answer 33

- Unsaturated fats have at least one C=C double bond whereas saturated fats have on single bonds. - Unsaturated fats have a lower melting point than saturated - Unsaturated -> usually from plants whereas saturated -> usually from animals