Revision notes topic questions past papers

glycerol molecule

Phospholipids are amphipathic (they have both hydrophobic and hydrophilic parts)

As a result of having hydrophobic and hydrophilic parts phospholipid molecules form

monolayers or bilayers in water

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CIE AS Biology (9700) 2019-2021 Revision Notes

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2. Biological Molecules

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Page 40

In the presence of water due to the hydrophobic and hydrophilic parts phospholipids will

form monolayers or bilayers

Role

The main component (building block) of cell membranes

Due to the presence of hydrophobic fatty acid tails, a hydrophobic core is created when a

phospholipid bilayer forms

This acts as a barrier to water-soluble molecules

The hydrophilic phosphate heads form H-bonds with water allowing the cell membrane to

be used to compartmentalise

This enables the cells to organise specific roles into organelles helping with efficiency

Composition of phospholipids contributes to the fluidity of the cell membrane

If there are mainly saturated fatty acid tails then the membrane will be less fluid

If there are mainly unsaturated fatty acid tails then the membrane will be more fluid

Phospholipids control membrane protein orientation

Weak hydrophobic interactions between the phospholipids and membrane proteins

hold the proteins within the membrane but still allow movement within the layer

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