Summary
Summary Biological Molecules - Lipids
- Institution
- AQA
Biological Molecules - Lipids
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LipidsLipids are made up of glycerol and fatty acids. There can be triglycerides and phospholipids.
Fatty Acids are made of hydrocarbons which are hydrophobic (repels water) at the tails. These
tails make lipids insoluble in water.
Saturated Fatty Acids do not have double bonds between their carbon atoms - unsaturated
fatty acids do which causes the chain to kink and curve.
Triglycerides: are mainly used as storage molecules (adipose tissue) due to their long
hydrocarbon chains of fatty acids which contain a lot of chemical energy so a lot of energy is
released when broken. They are also insoluble due to the fatty acid tails so osmosis doesn't
occur and the tails face inwards so the molecules are shielded by the glycerol heads.
Phospholipids are found in the cell membrane making up the bilayer. They have the same
structure as triglycerides but a phosphate molecule replaces a fatty acid. The phosphate group
is hydrophilic (attracts water). The fatty acid tail is hydrophobic repels water, because of this
they form a double layer with the head facing outwards and tails inwards repelling water so the
centre of the bilayer is hydrophobic.
In water they position themselves so the hydrophobic heads can interact with water but the
hydrophobic tails cluster away from water - this allows phospholipids to form membranes
around cells.
Test for Lipids: place the food sample in the test tube add ethanol, mix until dissolved. Then
add water. If a milky emulsion forms lipids are present.
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