Biological Molecules: Lipids

Question 1

What are lipids made from?

Answer 1

• Contain hydrocarbons and oxygen

Question 2

Are lipids polymers?

Answer 2

• No, lipids are not made of repeating monomers

Question 3

Are lipids soluble in water?

Answer 3

• Insoluble in water

- Soluble in organic solvents like ethanol

Question 4

What are the main types of lipids found in living things?

Answer 4

• Triglycerides

- Phospholipids

Question 5

How are triglycerides formed?

Answer 5

• Condensation reaction between 1 molecule of glycerol and 1 fatty acid
• Repeats with 2 other fatty acids to form a triglyceride
• Forms ester bonds
• Fatty acids can be saturated or unsaturated

Question 6

Describe the features of saturated fatty acids

Answer 6

• Saturated - no C=C bonds

• Saturated triglycerides are commonly known as fats
• Solid at room temperature

• C-C bonds mean fatty acid tails don’t bend

• More compact than unsaturated triglycerides
• Stronger intermolecular forces than unsaturated triglycerides
• Particles are more tightly packed and have stronger intermolecular forces - rigid and therefore, solid at room temperature

Question 7

Describe the features of unsaturated fatty acids

Answer 7

• Unsaturated - at least one C=C bond

• Unsaturated triglycerides are commonly known as oils
• Liquid at room temperature

• C=C bonds mean fatty acid tails bend

• This pushes other unsaturated triglycerides further away in the cell - less compact
• More space between unsaturated triglycerides mean intermolecular forces are weaker
• Particles can flow and have weaker intermolecular forces - liquid at room temperature

Question 8

Explain how triglycerides’ structure help in respiration

Answer 8

• Triglycerides can be hydrolysed into glycerol and fatty acids, which are also used in respiration
• Water - produced from respiration, triglycerides provide good source of water for metabolic reactions

Question 9

Explain how triglycerides’ structure helps them act as energy stores

Answer 9

• Triglycerides provide the most energy per unit of mass of any storage molecule

• Triglycerides contain a lot of chemical energy from large number of carbon hydrogen bonds within fatty acid tails
• Useful for animals, reduces the mass that must be carried around

• Insoluble

• Large and non-polar molecules, hydrophobic fatty acid tails
• Stored substance doesn’t dissolve
• They don’t affect the water potential of cells

Question 10

Explain how triglycerides’ structure helps them waterproof surfaces

Answer 10

• Triglycerides are insoluble in water so aquatic animals produce oil to waterproof their fur

Question 11

Explain how triglycerides’ structure helps them act as insulators

Answer 11

• Fats are used by animals as thermal insulation

- Triglycerides are slow conductors of heat

Question 12

Describe the role triglycerides have in protecting organs

Answer 12

• Fats are also used by animals to protect delicate organs e.g kidneys

Question 13

How are phospholipids formed?

Answer 13

• One phospholipid molecule contains one molecule of glycerol, two fatty acids and one phosphate-containing group
• Condensation reaction between glycerol and a fatty acid forms an ester bond

Question 14

What is the role of phospholipids?

Answer 14

• Make up the bilayer of cell membranes

- Cell membranes control what enter and leaves the cell

Question 15

Why are phospholipids polar?

Answer 15

• Phosphate heads are hydrophilic (loves water) and the tails are hydrophobic (hates water), meaning they are polar molecules

Question 16

Explain how phospholipids are an important part of cell surface membranes and form a barrier

Answer 16

• The hydrophilic heads of the phospholipids can be used to hold the surface of the cell surface membrane
• Centre of bilayer is hydrophobic, so water soluble substances can’t pass through easily