lipids

Question 1

contrast saturated and unsaturated fatty acids

Answer 1

saturated:
- contain only single carbon bonds
- straight chain molecules and have many contact points
- higher melting point = solid at room temperature
- found in animal fats
unsaturated:
- contain double carbon (C=C) bonds
- ‘kinked’ molecules and have few contact points
- lower melting point = liquid at room temperature
- found in plant oils

Question 1

how do triglycerides form? draw this

Answer 1

• condensation reaction takes place between 1 molecule of glycerol and 3 fatty acids which forms ester bonds
• (refer to images)

Question 2

relate the structure of triglycerides to their functions

Answer 2

• high energy:mass ratio = high calorific value from oxidation so acts as an energy store
• insoluble hydrocarbon chain = no effect on water potential of cells and is used for waterproofing
• slow conductor of heat = thermal insulation (e.g. adipose tissue)
• less dense than water = buoyancy of aquatic animals

Question 3

describe the structure and function of phospholipids

Answer 3

• amphipathic: glycerol backbone attached to 2 hydrophobic fatty acid tails and 1 hydrophilic polar phosphate head
• forms phospholipid bilayer in water = component of membranes
• tails can splay outwards = waterproofing e.g. for skin

Question 4

are phospholipids and triglycerides polymers? explain your answer

Answer 4

no - they are not made from a small repeating unit; instead they are macromolecules

Question 5

describe the structure and function of cholesterol

Answer 5

• steroid structure of 4 hydrocarbon rings
• hydrocarbon tail on one side, hydroxyl group (-OH) on the other side
• adds stability to cell surface phospholipid bilayer by connecting molecules and reducing fluidity