Biological molecules - LIPIDS

Question 1

What are the two groups of lipid?

Answer 1

Triglycerides and phospholipids

Question 2

How are triglycerides formed?

Answer 2

By the condensation of one molecule of glycerol and 3 molecules of fatty acid

Question 3

What type of bond does a condensation reaction between glycerol and a fatty acid form?

Answer 3

An ester bond

Question 4

How do fats form droplets?

Answer 4

Majority of a lipid is C-H, which is non polar (can’t form hydrogen bonds with water) -> hence it has London forces with adjacent triglycerides

Question 5

Why are lipids immiscible?

Answer 5

Lipids cannot form Hydrogen bonds and disperse in water

Question 6

What is the difference between saturated and unsaturated fatty acids?

Answer 6

• Unsaturated fatty acids contain at least 1 or more double carbon bonds
• Unsaturated fatty acids contain a kink caused by the C=C bond; hence they pack less closely together

Question 7

Why are unsaturated fatty acids more likely to be liquid?

Answer 7

• They contain a kink caused by the C=C bond
• This causes them to pack less closely together
• Hence there are fewer London forces between fatty acid chains
• And they are more likely to be liquid

Question 8

How does the length of the hydrocarbon chain affect the state of the lipid?

Answer 8

• More carbons mean there will also be more London forces
• Hence it is more likely to be a solid

Question 9

EMULSION TEST: why does the emulsion form?

Answer 9

• The ethanol hydrolyses the lipid molecule, breaking the hydrogen bonds and London forces
• Hence the fat disperses through the ethanol/water mixture/ mixture refracts light, so appears milky

Question 10

What are the differences between triglycerides and phospholipids?

Answer 10

• Triglycerides are non polar whilst phospholipids are polar and non polar
• Triglycerides have 3 fatty acids but phospholipids have 2 fatty acids
• Only phospholipids have a phosphate group

Question 11

Why is waterproofing important in tryglicerides? (STRUCTURE TO FUNCTION Q)

Answer 11

Triglycerides are non polar; hence not soluble in water. Water will not bead on the surface, nor will it diffuse between lipid molecules.

Question 12

Why is thermal/electrical insulation important in triglycerides? (STRUCTURE TO FUNCTION Q)

Answer 12

Triglycerides cannot become charged to lose electrons and there is relatively little movement within molecules; hence little energy transfer.

Question 13

Why is the fact they are respiratory substrates important to triglycerides? (STRUCTURE TO FUNCTION Q)

Answer 13

Triglycerides can undergo many oxidation reactions (loss of Hydrogen) in respiration to produce ATP.

Question 14

What does amphipathic mean?

Answer 14

If something is both hydrophilic and hydrophobic