3.1.3 Lipids

Question 1

Are lipids soluble?

Answer 1

• Insoluble in water
• Soluble in organic solvents
  … eg) alcohols and acetone

Question 2

two groups of lipid

Answer 2

• Triglycerides

- Phospholipids

Question 3

most common lipid

Answer 3

Triglycerides

Question 4

What are triglycerides also known as

Answer 4

Fats and oils

Question 5

3 other lipids

Answer 5

1) Waxes
2) Steroids
3) Cholesterol

Question 6

Difference between fats and oils?

Answer 6

1) Fats are solid at room temp (10-20 degrees C), oils are liquid at room temp

Question 7

What are lipids made up of?

Answer 7

Carbon
hydrogen
oxygen

Question 8

Polarity of lipids

Answer 8

Non-polar

so soluble in alcohol and acetone but insoluble in water

Question 9

Major biological role of lipids

Answer 9

Energy store

Question 10

Why are lipids a good energy store?

Answer 10

Stores over twice the amount of energy as carbohydrates
Lower proportion of oxygen to carbon and hydrogen than carbohydrates
so don’t react as easily

Question 11

Roles of lipids

Answer 11

1) Energy source
- When oxidised, lipids
… Release more than twice the energy as the same mass of carbohydrate
… Release water, which releases energy

2) Waterproofing
- Plants and insects have waxy cuticles
… Conserve water
- Mammals produce an oily secretion from the sebaceous glands in the skin
… Conserve water

3) Insulation
- Fats slow conductors of body heat, so stored beneath the body surface to retain body heat (reduce conduction away from body)
- Electrical insulators in the myelin sheath around nerve cells

4) Protection
- Stored around delicate organs
… ie) Kidneys

Question 12

Where are lipids stored?

Answer 12

Adipose tissue

Question 13

Role of lipids stored in adipose tissue

Answer 13

Heat insulation

protection

Question 14

Why aren’t triglycerides polymers?

Answer 14

Not made of monomers/many repeating units

Question 15

triglyceride structure

Answer 15

• 1 glycerol molecule

- fatty acid chains are attached via ester bonds

Question 16

Structure of triglycerides related to their properties

Answer 16

1) Good energy source
- Due to high ratio of energy-storing carbon-hydrogen bonds to carbon atoms

2) Good storage molecules
- Low mass to energy ratio
- Much energy can be stored in a small volume

3) Their storage doesn’t affect osmosis/water potential of cells
- As non-polar

4) Source of water for organisms
- Due to high ratio of hydrogen to oxygen atoms
- When oxidised, released water
… ie) Useful for organisms in dry deserts

Question 17

Give 2 features of a fatty acid molecule

Answer 17

• Long chain hydrocarbons

- Contain a carboxylic group (COOH) group at one end

Question 18

General formula of a fatty acid molecule

Answer 18

RCOOH

Question 19

formula for a fatty acid molecule

Answer 19

CH3(CH2)nCOOH

where n is usually an even number

Question 20

Triglycerides have a hydrophobic tail. Explain how this feature of a lipid is important for its function (2)

Answer 20

Hydrophobic tails cause lipids to clump together in cytoplasm as insoluble droplets (1)
So can be stored in cells as energy source without affecting cell’s water potential (1)

Question 21

Hydrophobic

Answer 21

‘Water hating’, a substance that repels water molecules.

Question 22

Hydrophilic

Answer 22

‘Water loving’, a substance that attracts water molecules.

Question 23

Phospholipid structure

Answer 23

one glycerol,
one phosphate containing group
two fatty acids

Question 24

Fluid mosaic model

Answer 24

…

Question 25

Why do phospholipid molecules form a bilayer

Answer 25

hydrophilic heads attract water ...point outwards towards water Hydrophobic tails repel water ...point inwards towards each other

Question 26

How does the phospholipid bilayer control the substances passing and out of the cell?

Answer 26

forms a barrier to water-soluble substances └e.g. sugars, amino acids and ions water can pass througg lipid soluble substances can pass through └e.g. oxygen and carbon dioxide

Question 27

Ester bond

Answer 27

The bond between glycerol and a fatty acid found in triglycerides and phospholipids.

Question 28

What group are fatty acids?

Answer 28

Carboxyl groups (COOH) with hydrocarbon tail (can be saturated/unsaturated)

Question 29

What can the hydrocarbon tail of a fatty acid vary in?

Answer 29

Length

Question 30

What does the R group stand for?

Answer 30

Saturated or unsaturated fatty acid

Question 31

Saturated fatty acid

Answer 31

Fatty acid with no C=C bonds, and therefore saturated with hydrogen.

Question 32

Unsaturated fatty acid

Answer 32

Fatty acid with one C=C bond. Can accept more hydrogen therefore it is unsaturated by hydrogen.

Question 33

Polyunsaturated fatty acid

Answer 33

Fatty acid containing two or more C=C (double carbon) bonds.

Question 34

What are the main differences in properties between saturated and unsaturated fatty acids?

Answer 34

Lipids containing saturated fatty acids are usually solid at room temperature (fats) lipids containing unsaturated fatty acids are generally liquid at room temperature (oils)

Question 35

Saturated fatty acids structure to function

Answer 35

- Only contain single bonds between carbon atoms ... Therefore can't add hydrogens to the carbons ... Which makes the molecule straight ... Which means molecules line up and bond easily ... Which makes saturated fatty acids a good energy store

Question 36

example of a saturated fatty acid

Answer 36

Stearic acid (CH3(CH2)16COOH

Question 37

What is one fatty acid molecule substituted for in a phospholipid?

Answer 37

Phosphate containing group

Question 38

Compare and contrast phospholipids and triglycerides

Answer 38

Phospholipids have two fatty acid tails but triglycerides have three. Both contain glycerol and fatty acids but phospholipids have phosphate groups in them too.

Question 39

properties of phospholipids related to structure

Answer 39

``` polarity forms lipid bilayer of cell surface membrane hydrophilic heads attract water ...point outwards towards water Hydrophobic tails repel water ...point inwards towards each other ``` Combine with carbohydrates at the cell surface membrane to form glycolipids - important in cell recognition

Question 40

test for lipids

Answer 40

emulsion test

Question 41

Emulsion test | lipids

Answer 41

add ethanol THEN add water shake gently positive result- cloudy white emulsion negative result- clear

Question 42

EQ: structure of a triglyceride

Answer 42

- contains glycerol - 3 fatty acids - forms 3 ester bonds

Question 43

EQ: Differences between triglyceride and phospholipid

Answer 43

Phospholipid has - phosphate - 2 fatty acids

Question 44

EQ: Unsaturated fatty acid

Answer 44

- double bonds | - between carbon atoms

Question 45

EQ: Describe how phospholipids are arranged in a plasma membrane

Answer 45

- in a bilayer - with hydrophobic fatty acid lipid tails on the inside - and hydrophilic polar phosphate group heads to the outside

Question 46

EQ: Describe how you could use the emulsion test to show the presence of oil in a sample of fish.

Answer 46

1. (Shake with) ethanol/alcohol; 2. Then add (to) water; 3. White/milky/cloudy (layer indicates oil);

Question 47

EQ: Explain why the pH decreases when the lipase is added to the milk

Answer 47

Fatty acids produced

Question 48

EQ: Suggest how the scientists may have treated the milk to remove lactose.

Answer 48

Add lactase