lipids Flashcards
Show how triglycerides are formed by condensation from glycerol and fatty acids
Lipids are formed by joining three fatty acid molecules to a glycerol molecule by condensation reactions. The bonds formed are known as Ester bonds.
3 h2O is removed
Give the structural formula of glycerol
…H
H-C-OH
H-C-OH
H-C-OH
…H
propane-1,2,3-triol
General formula of a fatty acid
.HO . H H H H H H H H H H H
O=C- C-C-C-C-C-C-C-C-C-C-C-H
………..H H H H H H HH H H H
Explain the difference between saturated and unsaturated fatty acids
SATURATED = no double bond between carbons in a hydrocarbon chain
UNSATURATED = there is a double bond between carbons in a hydrocarbon chain
Describe how a phospholipid is formed
Has a similar structure to triglycerides. However, one of the fatty acids is replaced by a phosphate group, so the glycerol combines with two fatty acids and one phosphate group.
phosphate groups is negative
makes phospho-glycerol head hydrophilic - attracts water
fatty acid tails are hydrophobic - repels water
This allows the phospholipids to form a bilayer in water.
Describe the ethanol emulsion test for lipids
- A small amount of the sample is placed into a test tube with 2cm3 of ethanol.
- The mixture is shaken so that the fat dissolves in the alcohol (non-polar solvent).
THEN
- Water is then added drop by drop and shaken again.
- A cloudy white emulsion (layer) of fat droplets should be visible if fat is present
Add ethanol to sample - then shake
Add water to sample - then shake
If white cloudy emulsion appears then positive test
describe triglycerides
Triglycerides are made from one molecule of glycerol joined by Ester bonds to three fatty acids. This is not a polymer because it is not made of the same/similar monomers.
2 key terms
glycerol head
fatty acid tail
between what 2 molecules is an ester bond formed ?
between a fatty acid and glycerol via a condensation reaction
