Lipids - Biological Molecules

Question 1

Describe the emulsion test for lipids

Answer 1

• dry and grease free test tube
• add ethanol to sample
• shake tube to dissolve
• add water and shake
• cloudy white colour indicates the presence of a lipid
• a negative test shown by a clear solution
  (if testing a sold crush/grind before dissolving)

Question 2

What elements do lipids contain?

Answer 2

Carbon, hydrogen and oxygen
But lower ratio of O to C and H than carbs

Question 3

Are lipids soluble?

Answer 3

Non-polar molecules
So insoluble in water
But soluble in alcohols and acetone (organic solvent)

Question 4

What are other properties of lipids?

Answer 4

Generally hydrophobic
Don’t form polymers

Question 5

What are the types of lipids?

Answer 5

Triglycerides - fats and oils
Phospholipids - found in cell-surface membrane

Question 6

How is triglyceride an energy + water source?

Answer 6

• energy and metabolic water source
• when oxidise provide more that twice the energy than the same mass of carbs and release valuable water

Question 7

How are triglycerides buoyancy aids?

Answer 7

• called blubber in aquatic animals and used a buoyancy aid
• less dense than muscle or bone

Question 8

How are triglycerides insulation?

Answer 8

• heat: slow conductors of heat
• electrical: myelin sheath around nerve cells helps speed up transmission of impulse

Question 9

How are triglycerides waterproof?

Answer 9

• insoluble in water and useful in providing waterproof protection
• mammals produce waterproof layer from skin

Question 10

How are triglycerides used as protection?

Answer 10

• fat stored around delicate organs e.g. kidney
• cuticle of lead

Question 11

What do triglycerides consist of?

Answer 11

3 fatty acids and glycerol (see notes for diagram)

Question 12

How is glycerol shown?

Answer 12

(See notes)
Sometimes written as

CH2OH
I
CH2OH
I
CH2OH

Question 13

What do fatty acids consist of?

Answer 13

Carboxyl group (COOH)
Hydrocarbon chain

Question 14

What do variations in properties come from?

Answer 14

As glycerol is always the same, variations in properties in different fats and oils come from variations in the fatty acids.

Question 15

What are fatty acids?

Answer 15

There are over 70 different fatty acids
All have an acidic COOH group and hydrocarbon chain attached (R group)

Question 16

What are saturated fatty acids?

Answer 16

Hydrocarbon chain has only single bonds (between carbon atoms)

Question 17

What are unsaturated fatty acids?

Answer 17

Hydrocarbon chain has at least one double bond (between carbon atoms)

Question 18

What are the properties of saturated fatty acids?

Answer 18

-long straight chains
- most animal fats
- solid at room temp

Question 19

What are the properties of unsaturated fatty acids?

Answer 19

-plant and fish fats
- vegetable oils
- liquid at room temp
- kinks made by double bonded C prevent molecules from packing tightly together

Question 20

What reaction takes place between fatty acids and glycerol?

Answer 20

A condensation reaction occurs between glycerol and fatty acids to form an ESTER BOND

Question 21

Where must water molecules come from in the condensation reaction?

Answer 21

H from OH group on glycerol
OH from carboxyl group on fatty acids
Must be from exact positions

Question 22

Explain emulsion test for lipids

Answer 22

Lipid will dissolve in ethanol
But will not in water -forming cloudy white emulsion

Question 23

How is structure related to function for triglycerides?
Pt 1

Answer 23

High proportion of C-H bonds for number of C atoms (bonds store energy)
- excellent source of energy

High proportion of H to O atoms
- release water when oxidised, so useful source of water (especially for animals living in dry climates)

Large non polar molecules making them insoluble
- storage doesn’t affect the water potential of the cell and so no effect on osmosis

Question 24

How is structure related to function of triglycerides?

Answer 24

Low mass to energy ratio
- good storage molecule because a great deal of energy can be stored in a small volume

Question 25

Draw condensation reaction between triglyceride and phosphoric acid to make a phospholipid

Answer 25

See notes

Question 26

What is the structural difference between a triglyceride and a phospholipid?

Answer 26

One of the fatty acids is replaced by a phosphate group
Shown as P

Question 27

What are the properties of phospholipids?

Answer 27

• phosphate is -vely charged and attracts water HYDROPHILIC
• fatty acid molecules are HYDROPHOBIC and repel water
• a phospholipid has a
  HYDROPHILIC HEAD
  HYDROPHOBIC TAIL

Question 28

What is the structure of a phospholipid?

Answer 28

Polar head
Attracts water
Hydrophilic

Fatty acid tails
Repels water
Hydrophobic

Question 29

What are the adaptations to function (phospholipid)? Bilayer

Answer 29

• polar molecule with hydrophilic head and hydrophobic tail with 2 fatty acids
• in aqueous environment molecules form a bilayer within cell-surface membrane
• forms a hydrophobic barrier between inside and outside of cell

Question 30

What are the adaptations to function (phospholipid)? Micelles

Answer 30

• can self-assemble into micelles
• useful in the absorption of molecules that aren’t easily soluble

Question 31

What are the adaptations to function (phospholipid)? Glycolipids

Answer 31

• structure allows them to combine with carbohydrates within cell-surface membrane to form glycolipids
• important in cell recognition