Lipids Flashcards
(22 cards)
Emulsion Test for Lipids
- Shake sample with ethanol in a test tube
- Then pour into a half filled test tube of water
- +ve result = milky white emulsion
The 4 Functions of Triglycerides
BIPE:
- Buoyancy
- Insulation
- Protection
- Energy Storage
Why can triglycerides be used for Buoyancy?
- Low density of adipose tissue (fat is less dense than water)
- Enables aquatic animals to float on water
Why can triglycerides be used for insulation efficiently? And give 2 examples of this.
MA:
- Very good insulators of heat
- Part of the composition of the myelin sheath around nerve fibres (insulation increases speed of transmission of electrical impulses)
- Part of the composition of the adipose tissue layer under the skin - acts against heat loss
How are triglycerides used for protection?
- Adipose tissue surrounds some organs eg the heart
- Contains stored triglycerides
- Which protect the organ from mechanical shock
How are triglycerides good for energy storage? [1]
- Long hydrocarbon chains - lots of C-C/C-H bonds
- These bonds are high in energy
Therefore triglycerides store 37kJ of energy per gram (carbs and proteins only store 17kJ/g) - Triglycerides contain very little Oxygen therefore are highly reduced
- Therefore triglycerides are easily oxidised during cellular respiration and release a lot of energy to produce ATP
How are triglycerides good for energy storage? [2]
- Oxidation of C-H bonds released large numbers of H2O molecules (metabolic water) during cellular respiration
- This water is retained by desert animals if there is no available liquid water to drink
- Bird and Reptile embryos a,so use this water (in their shells)
How are triglycerides good for energy storage? [3]
- Triglycerides are hydrophobic
- Therefore they do not affect the water potential of cells
- Therefore lots can be stored
How do mammals store triglycerides and how does it benefit them?
- As oil droplets
- In adipose tissue
- Helps them survive when food is scarce
How do plants store triglycerides? Are they solid or liquid at r.t.p? Why?
- In their seeds and fruit as oils
- Generally liquid
- Due to double bonds - most stored triglycerides in plants are unsaturated
Why are unsaturated fats usually liquid at r.t.p?
- Double bond adds kinks to the chain
- Therefore molecules are unable to pack closely together
- Minimising the vdW forces between the molecules
Why can triglycerides cross the PLB?
- Polar, hydrophobic
Which have lower boiling points, mono or polyunsaturated fats? Why?
- Polyunsaturated
- More kinks therefore they don’t pack as closely together
- Minimising effect of vdW forces between
Describe the structure of a phospholipid
- Glycerol molecule
- Bonded to 2 fatty acids
- And one phosphate “head”
Properties of a phospholipid
- Amphipathic
- As it has a polar, hydrophilic phosphate head
- And non-polar, hydrophobic FA tails
How do triglycerides and phospholipids form?
- Condensation reaction
- To form 3 ester bonds
- And 3 molecules of water are released
Why do phospholipids form bilayers but triglycerides don’t?
- Phospholipids are amphipathic
- Whereas triglycerides are fully hydrophobic
Role of Phospholipids in the CSM
- Main structural component
- Arranges in a bilayer
- To create a hydrophobic core that acts as a barrier to water soluble substances
- And a hydrophilic head region on both sides which forms H-bonds with water - allows the CSM to be used to compartmentalise
- Phospholipids also control membrane protein orientation by weak hydrophobic interactions - which hold the proteins within the membrane but still allow fluid movement within the bilayer
How does the composition of phospholipids contribute to the fluidity of the bilayer?
- The more unsaturated FAs there are in the bilayer, the more fluid it is (as there are more kinks so PLs can’t pack together tightly)
- The shorter the chains, the more fluid it is (as there are weaker vdW forces so PLs can’t pack together tightly)
Unsaturared fatty acid structure
- Methyl group at one end
- Variable region in the middle with at least one double C=C bond
- Carboxyl group at the other end
- Unsaturated = doesn’t contain the maximum amount of H atoms possible - more can be added
Why is partial hydrogenation of fats dangerous?
- Can make trans fatty acids
- Which can’t form enzyme-substrate complexes
- So can’t be digested
- And are linked to CHD
How are triglycerides stored inside cells
- As insoluble droplets
- Hydrophobic FA tails point inwards
- More hydrophilic glycerols point outwards
