Lipids

Question 1

Triglyceride Structure

Answer 1

1. 3 fatty acid molecules joined to 1 glycerol molecule, each by an ester linkage
2. Condensation reaction that produces 3 H2O
3. Produces a non-polar hydrophobic molecule due to long non-polar hydrophobic hydrocarbon chains attached to glycerol backbone, making them insoluble in water

Question 2

Glycerol and Fatty Acid Structure

Answer 2

• Glycerol has 3 polar hydrophilic hydroxyl groups
• Fatty acids are weak acids due to COOH group, but the longer the hydrocarbon chains, the less acidic and soluble they are
• Saturated fatty acids only have C-C single bonds
• Unsaturated fatty acids have C=C double bonds, cis ones have kinks

Question 3

Function (rmb to relate to structure if asked)

Answer 3

1. Major function of energy storage
   - Triglycerides release 2x as much energy as equivalent mass of carbs
   - Fats are less oxidised as they have a lower proportion of O and higher proportion of C-H bonds that contain energy
   - Fats are a more compact energy store, thus animals tend to store them more in adipose tissue while plants use starch (except for seeds)
2. Production of metabolic water
   - Important for desert animals to get water from food when external water limiting
3. Cushioning internal organs from mechanical damage
4. Thermal Insulation and Improving Buoyancy for marine mammals
5. Reservoir for Storage of Fat-Soluble Vitamins

Question 4

Structure of Phospholipids

Answer 4

1. 2 non-polar hydrophobic hydrocarbon tails and one negatively charged phosphate head attached to glycerol backbone by phosphoester linkage
2. Phospholipids are thus amphipathic w both hydrophilic and hydrophobic groups

Question 5

Phospholipid Function (link to Membranes Chapter)

Answer 5

Phospholipid bilayer makes up cell membranes
1. Hydrophilic phosphate heads face outwards to the aqueous environment
2. While hydrophobic hydrocarbon tails face inward to form a hydrophobic core
3. Phospholipid bilayer thus acts as a selectively permeable barrier between intracellular and extracellular environments
- Small non polar molecules can pass
- Small polar molecules like water pass through slowly via transient pores formed due to lateral movement and membrane fluidity
- Polar/Charged/Large molecules blocked
4. Compartmentalisation allows for formation of unique environments

Question 6

Structure + Function of Cholestrol

Answer 6

1. Cholestrol is slightly amphipathic, having hydrophilic hydroxyl group that has hydrophilic interactions with phosphate heads and hydrophobic fused ring that has hydrophobic interactions with hydrophobic core
   - Fused ring structure is also rigid and gives mechanical stability
2. Helps regulate membrane fluidity
   - At higher temperatures, it prevents membrane from being overly fluid by restricting phospholipid movement
   - At lower temperatures, it prevents membrane from being overly firm by preventing close packing of phospholipid
3. Helps to anchor proteins in membrane
   - Hydroxyl groups interact w hydrophilic R groups and fused ring interacts w hydrophobic R groups

Question 7

Ethanol Emulsion Test

Answer 7

1. Add 2 cm3 of ethanol to liquid/grounded and dissolved test sample. Mix well and stand for 2 min
2. Decant ethanol into test tube with 2 cm3 of water
3. Solution clear = no lipids; White emulsion = lipids
   - Ethanol extracts lipids from samples as its miscible, which become micelles in presence of water, diffracting light to appear cloudy white