1.5 Lipids Flashcards
How do triglycerides form? (3)
- Condensation reaction between 1 molecule of glycerol & 3 fatty acids
- Removes 3 water molecules (due to condensation reaction)
- Forms 3 ester bonds
Describe how to test for lipids in a
sample.
Add ethanol to the sample and shake (to dissolve the lipids) then add water
Positive result is a White emulsion
Contrast saturated and unsaturated fatty
acids
Saturated:
● Contain only single bonds
● Straight-chain molecules
have many contact points
● Higher melting point = solid
at room temperature
● Found in animal fats
Unsaturated:
● Contain C=C double bonds
● ‘Kinked’ molecules have
fewer contact points
● Lower melting point = liquid
at room temperature
● Found in plant oils
Relate the structure of triglycerides to
their functions
● High energy:mass ratio = high calorific value from
oxidation (energy storage).
● Insoluble hydrocarbon chain = no effect on water
potential of cells & used for waterproofing.
● Slow conductor of heat = thermal insulation e.g.
adipose tissue.
● Less dense than water = buoyancy of aquatic
animals.
Describe the structure and function of
phospholipids. (3)
- Glycerol backbone attached to 2 hydrophobic fatty acid tails & 1 hydrophilic polar phosphate head.
● Forms phospholipid bilayer in water =component of membranes.
● Tails act as waterproofing.
Compare phospholipids and
triglycerides.
● Both have glycerol backbone.
● Both may be attached to a mixture of
saturated, monounsaturated &
polyunsaturated fatty acids.
● Both contain the elements C, H, O.
● Both formed by condensation reactions.
Contrast phospholipids and triglycerides.
phospholipids:
● 2 fatty acids & 1
phosphate group attached
● Hydrophilic head &
hydrophobic tail
● Used primarily in
membrane formation
triglycerides:
● 3 fatty acids attached
● Entire molecule is
hydrophobic
● Used primarily as a
storage molecule
(oxidation releases
energy)
Are phospholipids and triglycerides
polymers?
No; they are not made from a small
repeating unit. They are
macromolecules.
Name the two groups of lipids
Triglycerides and phospolipids
Describe the structure of a fatty acid (RCOOH)
A straight chain of an even number of carbon atoms, with hydrogen atoms along the length of the chain and at one end of the chain and a carboxyl group (―COOH) at the other end
Describe the properties of triglycerides
(4)
- When oxidised they release water so they act as a metabolic water source (helps animals in the desert)
- They are large and insoluble so they do not affect water potential and cannot diffuse out the cell
- Lipids have a low mass so a lot of energy can be stored without increasing the mass
- Hydrophobic
Describe the differnece between the strcuture of triglycerides and phospholipids
One of the fatty acids of a triglyceride is substituted by a phosphate group in a phospholipid
What is the function of phospholipids?
Form a bi-layer in cell membrane allowing diffusion of lipid soluble(non polar) or very small substances and restricting movement of water soluble (polar) or larger substances
Descirbe how the properties of phospolipids relate to their strcture
Phosphate heads are hydrophillic-attrcted to water so point to water either side of membrane
Fatty acids tails are hydrophobic-repelled by water so point away from water to /interior of membrane
Due to the phosphate being charged it repels other fats
What are the charcteristics of lipids (5)
- Mainly made up of 4 elements:C O H
- Insoluble in water but soluble in organic solutions like alcohol and acetone
- Can be used as waterproofing:they are insoulble in water
- Insulation:fats are slow conductors of heat
- Protection:fat is often stored beneath the body to help body heat
