1.5 Lipids

Question 1

What is the solubility of lipids?

Answer 1

Insoluble in water
Soluble in organic solvents such as alcohols and acetone

Question 2

What elements are lipids made of?

Answer 2

Carbon, hydrogen and oxygen
The proportion of oxygen to carbon and hydrogen is smaller than in carbohydrates

Question 3

What are the two main groups of lipids?

Answer 3

Triglycerides (fats and oils) and Phospholipids

Question 4

What are triglycerides made of?

Answer 4

Glycerol and 3 fatty acids

Question 5

Draw the displayed formula of a glycerol

Question 6

Draw the displayed formula of a fatty acid

Question 7

How do triglycerides form?

Answer 7

Glycerol + 3 fatty acids —> (condensation) triglycerides (fat or oil) and 3H2O

Question 8

What is the bond in a triglyceride?

Answer 8

Ester bond formed by condensation reaction between glycerol and a fatty acid which centres around a shared oxygen atom

Question 9

Draw the displayed formula of a triglyceride

Question 10

Describe and draw the structure of an unsaturated fatty acid

Answer 10

Double bonds between carbons (C=C)
Shape is kinky/not straight

Question 11

Describe and draw the structure of a saturated fatty acid

Answer 11

-No C=C double bonds
-Saturated with hydrogens
-The fatty acids are straight, so can line up very closely together

Question 12

What is the difference between a polyunsaturated fatty acid and a mono unsaturated fatty acid?

Answer 12

Polyunsaturated - many C=C bonds
Monounsaturated - one C=C

Question 13

What do all fatty acids contain?

Answer 13

A carboxyl group (COOH) and a hydrocarbon of varying length-R

Question 14

How many hydroxyl groups does glycerol have?

Answer 14

3 hydroxyl groups (OH) and each may combine with different fatty acids in condensation reactions

Question 15

What is the structure of a phospholipid?

Question 16

What are the 4 roles of lipids?

Answer 16

Source of energy
Waterproofing
Insulation
Protection

Question 17

Explain how lipids are sources of energy

Answer 17

When oxidised, lipids provide more than twice the energy as the same mass of carbohydrates and release valuable water

Question 18

Explain how lipids waterproof

Answer 18

Insoluble in water so useful as a waterproofing
Both plants and insects have waxy, lipid cuticles that conserve water, while mammals produce an oily secretion from the sebaceous glands in the skin

Question 19

Explain how lipids insulate

Answer 19

Fats are slow conductors of heat and when stored beneath the body surface help to retain body heat
Also act as electrical insulators in the myelin sheath around nerve cells

Question 20

Explain how lipids protect

Answer 20

Fat is often stored around delicate organs e.g. the kidney

Question 21

Where do the differences in the properties of different fats and oils come from?

Answer 21

Variations in the fatty acids

Question 22

How is the structure of triglycerides related to their properties?

Answer 22

• High ratio of energy-storing carbon-hydrogen bonds: carbon atoms
• Low mass to energy ratio so good storage molecules because much energy can be stored in a small volume, reduces the mass animals have to carry as they move
• Large, non-polar molecules so are insoluble in water, so their storage does not affect osmosis in cells or the water potential of them
  -High ratio of hydrogen to oxygen atoms, so release water when oxidised

Question 23

What is the difference between a fat and an oil?

Answer 23

Oil is liquid at room temperature

Question 24

What is the difference between phospholipids and triglycerides?

Answer 24

The phosphate group replaces one of the fatty acid chains

Question 25

Is the phospholipid head hydrophilic or hydrophobic and why?

Answer 25

Hydrophilic (interact with water but not with fat) as negatively charged phosphate group attract water

Question 26

Is the phospholipid tails hydrophilic or hydrophobic and why?

Answer 26

Hydrophobic (repels water but mixes with fat)
Two non-polar hydrophobic tails (the fatty acid chains)

Question 27

Phospholipids are polar, what affect does this have?

Answer 27

Position themselves so that the hydrophilic heads are as close to the water as possible and the hydrophobic tails are as far away from the water as possible

Question 28

How are the structure of phospholipids related to their properties?

Answer 28

• Polar molecules, in an aqueous environment, phospholipid molecules form a bilayer in cell membranes therefore a hydrophobic barrier is formed between the inside and outside of a cell
• Hydrophilic phosphate heads of phospholipid molecule shell to hold at the surface of the cell-surface membrane
• Phospholipid structure allows them to form glycolipids by combining with carbohydrates in cell membranes (important in cell recognition)

Question 29

What do phospholipids form when mixed with water?

Answer 29

Droplet spheres (micelle) when mixed with water; the heads face the water and the tails face each other

Question 30

What is the test for lipids?

Answer 30

Emulsion test
- Add 5cm3 of ethanol to 2cm3 of the sample in a test tube
- Shake the tube to dissolve any lipid in the sample
- Add 5cm3 of water and shake
- A cloudy white emulsion colour means a positive lipid test