Biology revision - Lipids

Revision for OCR biology, lipids.

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  • Created on: 19-05-10 08:20
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Revision ­ Lipids
Triglycerides ­ Mainly used as energy storage molecules.
1. Long hydrocarbon tails of the fatty acids contain a lot of chemical energy ­ a load of energy
is released when they are broken down. Because of these tails, lipids contain about twice as
much energy per gram as carbohydrates.
2. They're insoluble, so they don't cause water to enter cells by osmosis. The triglycerides
bundle together as insoluble droplets in cells because the fatty acid tails are hydrophobic.
Phospholipids make up the bilayer of cell membranes. Cell membranes control what enters and
leaves the cell.
1. Phosphate head is hydrophilic and tails are hydrophobic, so they form a double layer with
heads facing outwards and tails facing inwards.
2. Centre of bilayer is hydrophobic so water-soluble substances can't easily pass through it ­
the membrane acts as a barrier to those substances.
Cholesterol molecules strengthen the cell membrane by interacting with the phospholipid bilayer.
1. Small size and flattened shape allows the cholesterol to fir in between the phopholipid
molecules in the cell membrane. They bind to the hydrophobic tails of the phospholipids,
causing them to pack more closely together helping the bilayer to become less fluid and
more rigid.


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