Lipids

Question 1

What elements make up lipids ?

Answer 1

C, H, O

Question 2

Are lipids soluble in water and organic solvents ?

Answer 2

Insoluble in water
Soluble in organic solvent

Question 3

Are lipids polar or non-polar ?

Answer 3

Non-polar and hydrophobic

Question 4

What are the three groups of lipids ?

Answer 4

Simple lipids
Complex lipids
Steroids and sterols

Question 5

How are simple lipids formed ?

Answer 5

By joining fatty acids to an alcohol by ester linkages

Eg. Triglyceride, waxes

Question 6

What are complex lipids made up of ?

Answer 6

A lipid and a non-lipid component

Eg. Phospholipids, glycolipids

Question 7

What are steroids and sterols characterised by ?

Answer 7

Carbon skeleton consisting of four fused rings (steroid nucleus)

Eg. Cholesterol

Question 8

What is a glycerol ?

Answer 8

An alcohol with three -OH groups

Question 9

Are glycerols soluble water ?

Answer 9

Yes - the OH groups can interact with water

Question 10

What are fatty acids ?

Answer 10

Long chained carboxylic acids contain an even number of carbon atoms
- consist of a long hydrocarbon chain (fatty acid tail) and a carboxylic acid group

Question 11

Which parts of te fatty acid are hydrophobic, which are hydrophilic ?

Answer 11

Long hydrocarbon chain is hydrophobic
Carboxylic acid is hydrophilic

Question 12

What does the melting point of difference fatty acids depend on

Answer 12

The degree of saturation and the length of the hydrocarbon chain

Question 13

What are saturated fatty acids ?

Answer 13

No C=C
Each carbon has maximum number of H atoms attached

Question 14

What are unsaturated fatty acids ?

Answer 14

C=C present creating a ‘kink’ in hydrocarbon tail

Question 15

As number of C=C increase, does MP increase or decrease ?

Answer 15

Decrease

Question 16

Why does MP decrease as number of C=C increase ?

Answer 16

Greater number of C=C means greater number of kinks
There is thus weaker intermolecular interaction between fatty acid molecules, lesser energy is required to weaken the hydrophobic interactions

Question 17

As length of hydrocarbon tail increase, does MP increase or decrease ?

Answer 17

Increase

Question 18

Why does MP increase when length of hydrocarbon tail increase ?

Answer 18

The longer the tail, the larger the surface area available for hydrophobic interactions between the hydrocarbon chains thus larger amounts of energy needed to weaken the interactions

Question 19

What makes up a triglyceride ?

Answer 19

1 glycerol + 3 fatty acids

Question 20

What is the bond joining the fatty acids to the glycerol in triglyceride ?

Answer 20

Ester bond

Question 21

How is triglyceride formed ?

Answer 21

Condensation reaction where a molecule of water is removed to form -COO- (ester bond)

Question 22

What are the five functions of triglyceride ?

Answer 22

1. Storage form of energy
2. Source of metabolic water
3. Good thermal insulator (blubber)
4. Provides buoyancy to aquatic mammals
5. Protective layer for delicate internal organs

Question 23

What properties of triglyceride allows it to be a good storage material ?

Answer 23

Large and uncharged hence insoluble in water
- can be stored in large amounts without affecting WP of cell and can be prevented from diffusing out of cells

Question 24

Why is triglyceride a good store of energy ?

Answer 24

For the same weight, triglycerides yields twice the quantity of energy compared to carbs
- lipids are more reduced than carbs, more oxidation steps are needed to fully oxidise lipids thus more ATP formed

Question 25

What is metabolic water ?

Answer 25

Water produced from oxidation of food, very important to desert animals

Question 26

Why are triglycerides a good source of metabolic water ?

Answer 26

Triglycerides yield 2x more H atoms than carbs thus better source of water - H atoms give water upon oxidation

Question 27

Why is triglyceride a good thermal insulator ?

Answer 27

Prevents excessive heat loss, important in aquatic animals

Question 28

Why does triglyceride provide buoyancy to aquatic animals ?

Answer 28

It is less dense than water

Question 29

what are phospholipids made out of ?

Answer 29

1 glycerol + 2 fatty acids + a phosphate group (negatively charged)

Question 30

How is phospholipids formed ?

Answer 30

Through 2 condensation reactions - one where fatty acid is joined to glycerol, forming ester bond and producing 1 mole of water - one where phosphate group is joined to glycerol, forming phosphoester bond and producing water

Question 31

What is a phospholipid ?

Answer 31

A complex lipid A major component of cell membrane

Question 32

Are phospholipids hydrophobic or hydrophilic ?

Answer 32

They are amphipathic (both hydrophobic and hydrophilic regions present) - hydrocarbon tails are hydrophobic - phosphate heads are hydrophilic

Question 33

What are the 4 functions of phospholipid ?

Answer 33

Form a bilayer due to their amphipathic nature Allows for compartmentalisation (separation) of cell contents from aqueous external cell environment Allows for formation of organelles within cell where specialised biochemical reactions occur Variations of phospholipids affect fluidity and thus permeability of membrane

Question 34

What is the structure of the phospholipid bilayer ?

Answer 34

Polar, hydrophilic heads point outwards and make contact with water molecules Non-polar, hydrophobic hydrocarbon tails point inwards, forming hydrophobic core

Question 35

How is a variety of phospholipids formed ?

Answer 35

Addition of small molecules to the phosphate group Degree of saturation Length of fatty acids