3.5 - Lipids

Question 1

Examples of lipids

Answer 1

Fats and oils

Question 2

What is a lipid

Answer 2

Molecule containing elements C, H, O.

Question 3

Why are lipids non polar

Answer 3

Electrons in outer orbitals that form the bonds are more evenly distributed than polar molecules. So no positive or negative areas within molecules and for this reason lipids are not soluble in water.

Question 4

What is a triglyceride

Answer 4

One glycerol molecule with three fatty acids

Question 5

What group of molecules does glycerol belong to

Answer 5

Alcohols

Question 6

What group of molecules do fatty acids belong to

Answer 6

Carboxylic acids. They consist of a (-COOH) Group with hydrocarbon chain attached

Question 7

What does glycerol have in common with the fatty acids that allows them to interact

Answer 7

Hydroxyl groups

Question 8

What happen when hydroxyl groups between glycerol and fatty acids interact

Answer 8

Three water molecules and Ester bonds are formed

Question 9

What is reaction between glycerol and fatty acids called

Answer 9

Esterification

Question 10

What type of reaction is esterification

Answer 10

Condensation reaction

Question 11

How do you break down triglycerides

Answer 11

3 water molecules are supplied to reverse reaction. Hydrolysis reaction.

Question 12

Saturated fatty acid

Answer 12

No double bonds present between carbon atoms. All carbon atoms form maximum number of bonds with hydrogen atoms.

Question 13

Unsaturated fatty acid

Answer 13

Double bonds between some carbon atoms.

Question 14

One double bond

Answer 14

Monounsaturated

Question 15

2 or more double bonds

Answer 15

Polyunsaturated

Question 16

Effect of presence of double bonds

Answer 16

Cause molecule to kink or bend so they can’t pack together as closely.
This makes them a liquid at room temperature rather than solids.
Described as oils.

Question 17

Type of triglyceride in plants

Answer 17

Unsaturated triglycerides, normally occur as oils. Tend to be more healthy in human diet than fats.

Question 18

What leads to coronary heart disease

Answer 18

Saturated fats. Evidence remains inconclusive as excess of any fat can lead to obesity which also puts strain on heart.

Question 19

What is a phospholipid

Answer 19

Modified triglyceride. Contains phosphorus, carbon, hydrogen and oxygen.

Question 20

Inorganic phosphate ions

Answer 20

Found in cytoplasm of every cell. Extra electrons, negatively charged, making them soluble in water.

Question 21

How are phospholipids modified

Answer 21

One of the fatty acid chains in triglyceride molecule is replaced with a phosphate group.

Question 22

How are phospholipids strange

Answer 22

Due to length, they have non polar tail (fatty acid chain) and a charged head (phosphate group). Non polar tails are hydrophobic and mix with fat, hydrophilic heads interact with and are attracted to water.

Question 23

Why are phospholipids called surfactants

Answer 23

They form a layer in surface of water with phosphate heads in water and fatty acid tails sticking out of water.

Question 24

Why are phospholipids good for forming cell membranes

Answer 24

They can form structures based on a two-layered sheet formation (bilayer).
Hydrophobic tails point toward centre, protected from water by hydrophilic heads
This allows them to separate aqueous environment in which cells exist from aqueous cytosol within cells.
It is thought that this is how first cells were formed, later on membrane-bound organelles within cells.

Question 25

What is a sterol

Answer 25

Steroid alcohol, another type of lipid found in cells.
They have dual hydrophobic/hydrophilic characteristics
Hydroxyl group is polar and hydrophilic, the rest of molecule is hydrophobic

Question 26

Example of a sterol

Answer 26

Cholesterol- body manufactures in liver and intestines.
Important role in formation of cell membranes, positioned between phospholipids with hydroxyl group at periphery of membrane.
Adds stability to cell membranes and regulates fluidity by keeping them fluid at low temperatures and stopping them from being too fluid at high temperatures.

Question 27

What is manufactured using cholesterol

Answer 27

Bile, vitamin D, steroid hormones

Question 28

Biological roles of lipids

Answer 28

Membrane formation
Hormone production
Electrical insulation necessary for impulse transmission
Waterproofing e.g. birds feathers and plants leaves

Question 29

Role of lipids for long term energy storage

Answer 29

Thermal insulation to reduce heat loss eg penguins
Cushioning to protect vital organs such as heart and kidneys
Buoyancy for aquatic animals like whales

Question 30

Identification of lipids

Answer 30

Emulsion test.

Question 31

How do you do the emulsion test

Answer 31

Sample is mixed with ethanol.
Resulting solution is mixed with water and shaken
If white emulsion forms later on top - lipid
If solution remains clear - negative result

Question 32

Problems with health advice

Answer 32

Validity of research not evaluated
Science not easy to explain
Difficult to isolate effects of one nutrient 
Data used in reports often flawed
Genetic differences

Question 33

Food synergy

Answer 33

Nutrients don’t work in isolation but as part of the combined effect of a whole range of nutrients.

Question 34

Example of food synergy

Answer 34

Whole grains have greater beneficial effect than any of their individual components
Combined effect of fish, fruit and vegetables that help prevent certain types of heart disease.